It feels like I've been writing about the Keystone XL pipeline since dinosaurs roamed the earth. I know I'm not the only energy journalist who is profoundly relieved the whole thing is over. All the arguments, pro and con, were made, remade, and re-remade long before Obama's decision was announced; the entire debate had taken on the air of exhausted kabuki.

There's probably not much more to add about the specifics. For details on why Obama rejected the pipeline, see Brad Plumer's post. Over at Politico, Elana Schor has assembled an excellent timeline tracing Keystone's tangled path. And don't miss Ben Adler's rich history of the activist campaign that ended in triumph yesterday.

It's activism I want to talk about.

There is a strain of hostility toward the Keystone campaign among Beltway wonks and journos that is, let's just say, underdetermined by the substantive critiques they offer. Take this high dudgeon from Stephen Stromberg on the Washington Post editorial page. He deems the campaign so "irrational and insulting," so "capricious and immature," that it "should have offended those who care" about clean energy. Lawsy mercy!

Nonetheless, it isn't all concern trolling. Plenty of people of good faith, even those who share a concern over climate change, are skeptical of, or at least puzzled by, the Keystone campaign. They all have versions of the same question: Why this? It doesn't seem like that big a deal in terms of carbon emissions. So why so much angst and organizing, so much wearying persistence, over this?

The question deserves an answer. Since this is likely my last post ever on Keystone, I'm going to do my best to answer it.

Don't worry, I'm not going to get into the Byzantine technical disputes over exactly how much this pipeline will or won't affect the economics of tar sands. It's clear enough that whatever the effect, it is going to be tiny relative to the scale of global oil production, certainly relative to the scale of climate change.

Instead, I want to unearth and examine of a few of the premises implicit in the critique, the charge that, in Stromberg's words, "anti-Keystone XL activists have misapplied their energy; the danger is that they will continue to do so."

Premise one: the goal of climate activism is to reduce carbon emissions

Many Keystone skeptics ("Keystone doubters"?) assume that the way to evaluate a climate activist campaign is by the carbon emissions it reduces. By that metric, Keystone seems an odd choice.

But it's an odd metric, if you think about it. And it speaks to the odd relationship the US political establishment has always had with climate change and climate campaigners.

The assumption has been that climate change is an "environmental issue" and that it is the job of environmentalists to fix it. It is the job of everyone else to tell them they are Doing It Wrong, to critique their methods, communication strategies, policy choices, and activist campaigns.

Anyone who understands the scale of the climate challenge ought to view this implicit arrangement with bafflement. The idea that one underpowered, underfunded faction of the US left, with all its cultural and institutional baggage, should or could be responsible for the climate portfolio is ludicrous.

It is also ludicrous to imagine that the primary goal of climate activist campaigns is to reduce emissions. It would be like criticizing the Montgomery bus boycott because it only affected a relative handful of black people. The point of civil rights campaigns was not to free black people from discriminatory systems one at a time. It was to change the culture. "Keystone isn’t a perfect battlefield," wrote Michael Grunwald, "but neither was Selma or Stonewall."

Premise two: Activists should target demand rather than fossil fuel supply

This follows from the first. if the goal of activist campaigns is to reduce emissions, then they are wasting their time fighting fossil fuel extraction and transport projects. The only way to get big, reasonably verifiable carbon emission reductions is through demand-side policies — renewable energy mandates, efficiency standards, carbon pricing, and the like.

Thus, the Doing It Wrong Brigade says, activists should be stumping for demand-side policy.

As I once wrote, this confuses wonk logic and activist logic. You can't just target any old thing and then build an campaign around it. This is what critics never got about the Keystone campaign: It was not some ready-built tool that was used on one thing and could easily have been turned to something else. It was a small miracle, a confluence of currents, lightning in a jar, what have you. You think Bill McKibben ever had an inkling all this would unfold?

The kind of movement that rose up around Keystone is not something you can plan or schedule. It's as much art, or, hell, magic, as science.

For whatever reason — a lot of tenacity, luck, and good timing — Keystone sparked something. Hundreds of thousands of people got engaged. If VSPs think they can get hundreds of thousands of people in the street for a revenue-neutral carbon tax, they are welcome to try.

Climate change is inherently difficult to organize around; it's big, abstract, and incremental. By the same token, broad, economy-wide policies to address it are also big, abstract, and incremental.

Supply-side fossil fuel projects compensate for some of the natural disadvantages of organizing around climate. They offer clear villains, unambiguous markers of success, and local impacts that help draw support from other affected communities and demographics — climate change can serve as the organizing concern, but not the only one (unlike, say, a carbon tax, for which climate change is the only motivation). The Keystone campaign was not only the largest ever movement organized around climate change in the US, it was also the most diverse. That's because Keystone was about more than climate; it was also about local pollution, political corruption, and corporate bullying.

This helps explain why climate activism has primarily manifested as "Blockadia" — blocking and shutting down bad projects is easier to organize around than efficiency or carbon pricing.

And maybe that's fine. Maybe it isn't the role of activists to imagine and bring about a new world. Maybe that's for policymakers, designers, engineers, artists, and entrepreneurs. Maybe the highest and best use of activism is just to make things uncomfortable, and more expensive, for the bad actors benefiting from the unsustainable status quo.

Premise three: reducing emissions is the only reason to fight supply-side battles

This also follows from the first two. If the metric of success is emission reductions, and emission reductions from supply-side fights are uncertain, then there's no point in fighting supply-side projects.

This assumes that emission reductions are the sole reason to go after the supply side, and thereby, I think, fundamentally misses what activists are trying to do. It's not to reduce emissions, one project at a time. It's to change culture.

This is perhaps the most important thing critics miss: all the ongoing climate activist campaigns — divestment, the "thin green line" fighting fossil fuel exports in the Pacific Northwest, the "stranded assets" push in the financial world, the whole "keep it in the ground" movement that's gathering steam, the #ExxonKnew investigations — are ultimately aimed at the same goal. They seek to remove the social license enjoyed by fossil fuel companies.

One part of transitioning to a new world is actually building parts of it. That's happening now: With renewable energy, electric cars, and smarter grids starting to come together, it's at least possible to see ahead, however dimly, to a world that's not dependent on fossil fuels. There are new and better alternatives now, which is a key political and messaging asset.

But the other part of transitioning to a new world is contesting the legitimacy of the old one. That means taking assumptions, institutions, and technologies that have a presumptive social warrant — that are assumed necessary, legitimate, and worthwhile by default — and, God help me for using this word, problematizing them.

Fossil fuel extraction and transport projects have a presumptive social warrant. Local opposition or environmental standards may sometimes trump that warrant, but the heuristic applied defaults to positive, to yes.

That attitude simply isn't commensurate with the urgency that climate change imposes. Limiting global temperature rise to 2 degrees means not burning 80 percent of the fossil fuel reserves already available to us. At the rate we're going, we're going to burn through that 20 percent in just a few decades. There have got to be some decisions made somewhere not to dig it up, not to build distribution infrastructure for it — to leave it in the ground.

Getting there means removing that presumptive social warrant, the default yes. It means creating a new heuristic: Fossil fuels must be reduced as fast as practically possible. It means creating a new default answer to fossil fuel infrastructure: no, unless a case can be made that the climate damage is worth it. This wouldn't mean cutting off all fossil fuels tomorrow, despite the crude caricatures painted of activists. But it would mean steadily raising the bar, changing a defeasible presumption of innocence to a defeasible presumption of guilt.

Activists have achieved more toward that goal than I would have thought possible, in a shorter time than anyone expected. They got Obama to say that he would only approve Keystone if it could be shown that it wouldn't damage the climate. Whether the administration applied that test correctly in this case is less important than the test itself, a new heuristic that is taking hold and working its way into the federal bureaucracy. Leaving some fossil fuels in the ground is now on the table, a live option.

Why this line in the sand? Why not?

In the end, the only answer to "why this?" is, why not this? If you want to draw a line in the sand, there's no point looking for a line that's already there. This was as good a line as any — it was ready to hand, and the outcome was purely under Obama's control.

It is true that each individual fossil fuel project is only a tiny contributor to the totality of climate change. But the industry as a whole is a high-functioning, high-earning, high-influence death machine that is driving civilization toward disaster, knowingly so. Some sand has got to be thrown in the fucking gears.

That's what the Keystone campaign was, what all supply-side campaigns are: sand in the gears. The question is not what effect this particular pipeline loss will have on this particular fossil fuel source. The question is, what effect will it have on fossil fuel investors to realize that any new supply-side proposal risks being met with a loud and furious grassroots movement that has hundreds of thousands of people on its mailing lists and a few high-profile victories under its belt?

What effect will it have on the economy, and on society, when fossil fuel companies lose their social license?

I honestly don't know. Social change is nonlinear and devilishly hard to predict. But it seems far from futile or pointless. It seems like an important part of the most important fight in the world.