In Los Angeles, the Museum of Contemporary Art (MOCA) is hosting the "first major U.S. museum survey of graffiti and street art." Sponsored in part by Nike and Levi's, "Art in the Streets" celebrates a form of cultural expression that America has collectively spent hundreds of billions of dollars trying to suppress during the last 40 years. Naturally, the exhibition has been generating controversy, and it will continue to do so when it moves to the Brooklyn Museum in March 2012.

City Journal's Heather Mac Donald has offered the most biting critiques of the show's contradictions and hypocrisies. She reports that MOCA is selling designer spray paint in its gift shop but doesn't allow visitors to bring that paint into the venue itself. She quotes former graffiti writers who are incredulous that she'd ask them whether they'd consider tagging their own homes. ("Why would you want to fuck up your own area?" one replies.) She contrasts street artists' platitudes about resisting capitalism with their brand licensing deals. She marvels that a show that romanticizes illegal behavior has so little to say about the behavior's economic and other costs.

But if it's true that "Art in the Streets" paints a phenomenon as charged and multidimensional as graffiti in the standard monochromatic hue of rebel deification, it's also true that graffiti is a phenomenon that institutions like MOCA ought to be taking on. After all, if graffiti really were nothing more than vandalism, it would neither be so attractive nor so objectionable to so many people. Nike hasn't sponsored any exhibitions devoted to the art of smashing mailboxes. MOCA has yet to show any interest in celebrating the cultural achievements of people who let their dogs defecate on your lawn. For ages, graffiti has been delighting its adherents, enraging its foes, and above all persisting, foreshadowing other aspects of our culture and expanding its scope.

In The History of American Graffiti (Harper Design), a comprehensive and entertaining look at how scribbling one's nickname on forbidden territory has evolved into a vibrant worldwide subculture, the art historians Roger Gastman (who helped curate the "Art in the Streets" show) and Caleb Neelon place the beginning of contemporary graffiti in the late 1960s. Graffiti, of course, existed for thousands of years before that, and in the 20th century various forms were flourishing well before a Philadelphia teenager named Cornbread and a New York kid who called himself Taki 183 began marking up the walls of their respective cities. Indeed, in midcentury Paris, communist-inspired graffiti was so common that chemists devised a special detergent to combat it and anti-graffiti teams equipped with ladders and alpine equipment were specially trained to remove it from the city's most hard-to-reach spots. By the mid-1960s, advertisers had started to co-opt graffiti. A popular Winston ad depicted a man leaning out a bus window and amending Winston's standard slogan with a paintbrush.

Around the same time, dissident college kids were also gravitating toward graffiti. In the French revolt of 1968, Parisians produced enough of it to fill an anthology titled The Walls Speak. But Cornbread and Taki 183 weren't interested in expressing political opinions or cynical wisecracks. They simply signed their names, as often as possible, in as many different parts of their cities as they could cover.

In The History of American Graffiti, an adult Taki 183 explains that part of his inspiration came from the campaign stickers, posters, and placards that politicians used to saturate the subway with. "They're putting it everywhere," he says. "So why shouldn't I? That was my sixteen-year-old rationale."

In other words, contemporary graffiti emerged not as an alternative to advertising but as an emulation of it. And DIY advertising could be just as effective as the professional stuff. By 1971 Taki 183 had forced his brand name into the consciousness of New York so effectively that he'd spawned hundreds of imitators and attracted the attention of The New York Times. By 1972 his imitators had spawned so many imitators of their own that Metropolitan Transportation Authority officials dolefully announced that every one of the subway system's cars had been marked with graffiti.

The subsequent competition for space and attention prompted rapid innovation. Writers began to work on a larger, more ambitious scale, with the intent of creating pieces so dazzling they could not be lost in the deluge. "The kids of New York…quickly realized that the factory-issue nozzles that came on spray paint were not optimal," Gastman and Neelon explain. But the nozzle from a brand of oven cleaner allowed them to achieve broader paint coverage. The nozzle from a brand of clear coating provided finer control when doing detail work.

Pretty soon, writers were covering entire subway cars, inside and out. Their audacity was amazing, their compositions increasingly sophisticated. Or at least some of them were. In an era when most kinds of cultural expression were still tightly monitored by vigilant gatekeepers, graffiti artists faced literal gates to crash, fences to scale, dangers to avoid. In 1974 one writer was decapitated by a moving train. Another burned to death after his spray can exploded. Two more were electrocuted.

But at least there were no editors, no label executives, no gallery owners saying, "Sorry, kid, your work's not fit for public consumption." If you managed to get your work up on a train, people would eventually see it. In this respect, graffiti outdid the Internet. Sites like YouTube offer access to anyone, but they can't guarantee an audience.

Graffiti can. Like billboards and other forms of outdoor advertising, it's fundamentally intrusive, and that is why, even though the opportunities for cultural expression have expanded exponentially since the 1970s, and even though the penalties for drawing pictures on other people's property can be severe, it continues to proliferate. Graffiti seizes viewer attention at a time when viewer attention is the scarcest resource in the world.

Of course, this quality is also what can make graffiti as oppressive as propaganda, as mundane as car insurance ads. Take it off the streets and graffiti becomes, in terms of discourse at least, a less totalitarian, more daring proposition. In galleries and museums, in books and on product packaging, it becomes easy to ignore, easy to reject, and thus more compelling in its effort to claim a share of our cultural landscape.

Contributing Editor Greg Beato (gbeato@soundbitten.com) writes from San Francisco.