Dave Foreman, cofounder of Earth First!, has been semiretired from the eco-vigilante business since the day four FBI agents burst through the front door of his Tucson, Arizona, home, ran to the bedroom, and leveled their .357s at him as he woke. It was 1990. An undercover FBI agent and provocateur, Michael Fain, had infiltrated an Arizona ecoterrorist group, Emetic (an acronym for Evan Mecham Eco Terrorist International Conspiracy), and had suggested that the members might like to bring down a transmission tower from the nearby Palo Verde Nuclear Generating Station. The Emetic people were happy to oblige. Foreman had no direct involvement in the attempted sabotage, but he was charged with conspiracy. He pleaded guilty to a misdemeanor, the crime of having given two inscribed copies of his book Ecodefense and a $100 donation to Agent Fain. Further vigilantism was now inadvisable; his conviction effectively rendered him hors de combat. In the years since, he has had to leave his monkey wrench at home, or so he says.

He remains the grittiest and most eloquent defender of wilderness we have. Foreman is one of the fathers of the rewilding movement and a leading proselytizer for Big Wilderness, for the Greater Yellowstone Ecosystem, for protecting and reintroducing large carnivores, and for corridors connecting wilderness areas in patterns that make for ecologically coherent wholes.

This year—the 50th anniversary of the Wilderness Act—skeptics have used the occasion to renew old attacks and to polish new ones. At the birthday party for wilderness, these crashers have been peeing freely in the punch bowl, and Foreman is roused. At the National Wilderness Conference in Albuquerque, New Mexico, on October 15, he will deliver a keynote.

Foreman does not do well in organizations, he has finally realized—not in the Wilderness Society, where he worked in the 1970s, or even in the free-form, nonhierarchical disorganization that is Earth First! In their place, he has invented an imaginary fraternity, or clan, that he calls the Cannots. The name comes from the opening sentence of Aldo Leopold’s classic A Sand County Almanac: “There are some who can live without wild things and some who cannot.”

I myself am a Cannot. I never joined, exactly—nobody does. I was absorbed as a toddler, or drafted, more like it, when Foreman was still in diapers and I was barely potty trained. My father was David Brower, the first executive director of the Sierra Club, founder of Friends of the Earth, the League of Conservation Voters, and the Earth Island Institute. He was an early king of the Cannots.

For eight years starting in 1955, my father and his closest colleague, Howard Zahniser of the Wilderness Society, worked together toward passage of the Wilderness Act. Zahniser was the bill’s author, and my father occasionally joined him at his favorite table at the Cosmos Club, in Washington, D.C., to help polish the language. My siblings and I got regular progress reports, and we were witness to the long, hard march of the legislation into law. My old man was the fieriest environmental evangelist of his generation, and he brought that evangelism home, practicing his powers of persuasion on us—as if those needed honing. During hikes in the Sierra Nevada, at the dinner table, and on the road, he drummed the poetry and logic of the wilderness idea into us. And he talked wilderness politics. One lesson, repeated often, had to do with the asymmetric warfare between exploiters and preservationists. “They only have to win once,” he would say. “We have to win every time.”

The price of wilderness is eternal vigilance by the people who love it.

Wilderness is like pornography. There are minor problems of definition, but as Justice Potter Stewart said of the hardcore stuff, “I know it when I see it.” At nine years old, I knew wilderness when I saw it. And so does most everyone else.

The Wilderness Act had powerful opposition from its inception. The major grazing, timber, and mining interests of the West took aim when the law was just a gleam in the eyes of Bob Marshall, Margaret Murie, Polly Dyer, and the others who conceived it. The rhetoric of the opposition in the 1950s and 1960s was that conservationists (as environmentalists then were called) wanted to “lock up” natural resources. This was true. To save a few unspoiled American landscapes for the benefit of the American people, and for the sake of those landscapes themselves, a few such places had to be locked away from the extractive industries and other despoilers.

Somehow the tree huggers won. The stockmen, loggers, miners, and developers, to their own amazement, lost, but they have never given up the fight. Throughout the 50 years of the Wilderness Act, there has been ceaseless effort to undermine it: the Sagebrush Rebellion, the Wise Use Movement, and various imitation groundswells of fake populism that have gone unnamed, like the present campaign by the oil billionaires of the Koch family to privatize public lands (the Koch Insurrection?), among others. The same forces have been at work to emasculate the Endangered Species Act, the Clean Air Act, the Clean Water Act, the Wild and Scenic Rivers Act, and the Environmental Protection Agency since they originated. And so it will be forever.

Lyndon Johnson’s signature was scarcely dry on the Wilderness Act before a second group joined the attack. This was a cadre of academics who questioned the very idea of wilderness. (Not the Sagebrush Rebellion of leathery ranchers in Stetsons, but an Ivy Rebellion of pale men in tweed with leather patches at the elbows.) These scholars contended that wilderness was just an abstraction, illusory, a construct. The deconstructionists, Dave Foreman calls this breed. Their dogma has brought to the study of environmental history what deconstructionist theory brought to English departments across the land: surpassingly beautiful subject matter—great works of literature on the one hand, wilderness on the other—is subjected to barren formulas and rendered a wasteland.

The ideas of the wilderness deconstructionists seem to be catching on today. Taken up by some historians of the environmental movement, the ideas have spread to a certain segment of the public. Deconstructionist theory now divides the movement itself, separating wilderness preservationists from newer breeds of environmentalists, like the foodie and smart-agriculture faction, whose hearts are in managed landscape (not in wild and unmanaged country), and from some environmental-justice advocates, who, in their focus on the disproportionate suffering of the poor from pollution and environmental degradation, sometimes view wilderness as an elitist concern.

Among the more vocal deconstructionists is professor William Cronon of the University of Wisconsin—Madison. This institution—bitter irony—is where Aldo Leopold taught. Cronon is emphatically not a Cannot. He is a proud chieftain of the Cans. Cronon’s essay “The Trouble with Wilderness; or, Getting Back to the Wrong Nature” has served as the wilderness deniers’ Magna Carta. In it he argues:

The more one knows of its peculiar history, the more one realizes that wilderness is not quite what it seems. Far from being the one place on earth that stands apart from humanity, it is quite profoundly a human creation—indeed, the creation of very particular human cultures at very particular moments in human history. It is not a pristine sanctuary where the last remnant of an untouched, endangered, but still transcendent nature can for at least a little while longer be encountered without the contaminating taint of civilization. Instead, it’s a product of that civilization, and could hardly be contaminated by the very stuff of which it is made. Wilderness hides its unnaturalness behind a mask that is all the more beguiling because it seems so natural. As we gaze into the mirror it holds up for us, we too easily imagine that what we behold is Nature when in fact we see the reflection of our own unexamined longings and desires.

This is nonsense in every particular. It presents itself as fresh, bold, and original thinking, but there is nothing original in it. Cronon is simply borrowing, and applying to wild places, the deconstructionist principles that Jacques Derrida developed in his study of ontology, and that his American followers borrowed, in their turn, and applied to literature. A prominent Derridean, J. Hillis Miller, explains: “Deconstruction is not a dismantling of the structure of a text, but a demonstration that it has already dismantled itself. Its apparently solid ground is not rock, but thin air.” Wilderness might look like something to you and me, Cronon echoes, but there is really nothing there.

Cronon disabuses us of the notion that wilderness is “untouched,” as we imagine. But how many of us actually do imagine that? It is not exactly news that humans are a wandering species and that, ever since the Paleolithic era, we have hunted and gathered nearly everywhere, touching nature wherever we went. “Pristine sanctuary?” You certainly won’t find any such claim in the Wilderness Act. There is no prohibition on human presence, past, present, or future, in the language of this law.

A little parable from my own life: As a boy, in what would become the John Muir Wilderness of the Sierra Nevada, following my father up to high passes over which the Paiutes traded, I would find sites where they had paused to pressure-flake obsidian arrowheads. You could find dozens half-finished. Some were almost perfect until a misplaced blow of the knapping tool—in the 1830s or the 1590s, or back before Columbus—had ruined them. The fletcher tossed those aside. Centuries later, a small boy picked them up, and someplace I have a cigar box heavy with obsidian fragments to prove it. Somehow the small boy was able to distinguish these half-buried artifacts from, say, a Sierra ski resort with its lifts rumbling or a six-lane highway with exits to malls.

Yes, some tribes set fires to keep meadows open. Sure, there is evidence that the earliest Amerindians, flakers of the Folsom point, a spear tip found in association with mammoth bones, may have helped ease the Pleistocene megafauna down the road to extinction. But how can these aboriginal impacts be compared, as the deconstructionists routinely do, to the transformation of the planetary surface and atmosphere wrought by technological civilization?

Wilderness is like pornography. There are minor problems of definition, but as Justice Potter Stewart said of the hardcore stuff, “I know it when I see it.” At nine years old, I knew wilderness when I saw it. And so does most everyone else.

Professor Cronon seems to have visited wilderness—or, as he insists, “wilderness”—but his writing is full of hints that he was never really present there. His argument, and that of the other wilderness deconstructionists, could only be the creation of academics with their heads up their own abstractions. It is healthy to pull one’s head out occasionally to sniff the actual sagebrush and cedar.

What wilderness travelers always seem to bring back from the wild—just as surely as near-death survivors bring back tales of light at the end of a tunnel—is a sense of having encountered something true, organic, and whole. What deconstructionists bring back from their reading of theory is exactly the opposite, their sense of a morass of incompatible meanings and no truth at all.

No wonder the two camps don’t get along.

In a July opinion piece in The New York Times, Christopher Solomon, who has fallen under the spell of the deconstructionists, argued that the Wilderness Act was fine for its time, 50 years ago. “In recent decades, however, several pillars upon which the act was built have eroded. One is the idea of ‘naturalness,’ that nature exists in some unadulterated state apart from humans. Work in paleoecology and other fields has shown that humans have shaped many of the ecosystems on the planet for thousands of years (and not always to their detriment). Research has also dismantled ideas about a stable, primeval world. Nature is always in flux.”

This is a massacre of history. The Wilderness Act was built on none of the pillars Solomon describes. The authors of the act were perfectly aware that nature had been adulterated almost everywhere by humans—this awareness was, indeed, their motivation in creating their law. Work in paleoecology and other fields “in recent decades” was not necessary to show that humans have shaped many ecosystems for thousands of years. We have the firsthand testimony of the ancient Sumerians and Greeks and Chinese who were on hand to witness the destruction of those ecosystems. Research of recent decades was not needed to dismantle ideas on a stable, primeval world. Those ideas were dismantled by (among others) the geologist James Hutton in the 18th century and by Charles Darwin and Alfred Russel Wallace in the 19th. The Darwin-Wallace theory of evolution, published more than 100 years before the Wilderness Act, is entirely dependent on the fact that “nature is always in flux.”

The 1960s were not the Dark Ages. The Age of Enlightenment did not begin 40 years ago. The authors of the Wilderness Act were not playing with half a deck.

There are objective threats to wilderness and the Wilderness Act, like H.R. 4089, the Sportsmen’s Heritage Act, which would open up wilderness to drilling and ATVs, and H.R. 1581, the Wilderness and Roadless Area Release Act, which would strip protection from nearly 60 million acres of the nation’s wildlands. But the greater danger, I think, is subjective: the erosion of the wilderness idea. The vitality of the idea, and belief in it, is what got us our wilderness system. Howard Zahniser and his 1960s colleagues sold Congress, President Johnson, and the American people on the idea. We now have 110 million acres of designated wilderness as a consequence. If the idea gets compromised, then wilderness loses its constituency. That constituency is necessary if we are to turn back all the H.R. 4090’s and H.R. 1581’s that lie ahead. The extractive industries only have to win once. We have to win every time.

For any number of reasons, I wish my father were alive to celebrate the 50th anniversary of the law he helped pass. He could team up again with Dave Foreman and work all the birthday conferences and festivals. The two men had great mutual admiration and occasionally performed together in a dog and pony show. Separately, either man could really work a room, and together it made for a tent revival. My father at some point would tell his Russell Train story. (Judge Russ Train, the head of the EPA under Nixon and a friend of my father’s, had once said of my old man, “Thank God for Dave Brower, he makes it so easy for the rest of us to appear reasonable.”) My father took this as high praise. He would repeat it, immodestly, to the crowd and then gesture across the dais at Foreman. “And thank God for Dave Foreman! He makes it so easy for me to appear reasonable. Now we need someone to make Dave Foreman appear reasonable.”

Both men adamantly opposed any compromise, equivocation, or reasonableness in the fight for wilderness and the wilderness idea.

Foreman would always end the session by howling like a wolf. Throwing back his head to sing, he would wave at the audience to join in. Sometimes there was self-consciousness in the chorus at the start, but the sound would gather and swell, louder and louder, a joyous yipping and ululation that shook the building.

Now that is how we should be celebrating the Wilderness Act.

Kenneth Brower specializes in environmental issues and natural history. He is the author of The Starship and the Canoe, Wake of the Whale, A Song for Satawal, Freeing Keiko, and The Wildness Within: Remembering David Brower, among other books. He lives in Berkeley, California.