Why do I think that? Put as simply as possible, I don't see how the intervention makes anything worse. Almost every negative consequence that could occur after our intervention -- collapse into tribal warfare, slaughter of civilians, destabilization of the region, Qaddafi winning anyway, Qaddafi retaliates against the West, the end of the so-called Arab Spring -- could also occur in the absence of intervention.
I think you have to keep that basic range of possibilities in mind when you analyze the potential consequences of military action. A lot of the war's opponents aren't doing that. For instance, earlier, I heard Dennis Kucinich talking about how forestalling Qaddafi's advance might create a haven for anti-American extremism in Eastern Libya. He's right! It might! But that was also true two weeks ago, when everyone thought Qaddafi was days away from falling. And yet somehow I doubt that, two weeks ago, Dennis Kucinich was hoping that the dictator would stage a comeback.
A lot of stuff that I've been reading about Libya from respectable sources (Dennis Kucinich is, admittedly, an easy target) relies on a similar slight-of-hand: now that the US has intervened, the author complains about a downside risk, without mentioning that A. the exact same risk existed prior to intervention, and B. very often, the risk is one that would accompany the author's preferred outcome; i.e., the rebels winning. There's this weird sense that now that we've intervened, Qaddafi winning would not be such a bad outcome, so no one could blame any of the ensuing badness on us.* But up until very recently, everyone seemed convinced -- and I don't really know anyone who disagreed on this fundamental point -- that post-Qaddafi chaos was a risk worth taking, just to be rid of the guy. I don't see why that calculus has suddenly changed for a lot of people, other than an irrational desire to avoid any ethical stake in the outcome. A failed intervention doesn't make the rebels any more dead, but a successful intervention has the potential to save a lot of lives.
And of course, there's my one enormous caveat: this is only valid so long as the American role in war doesn't significantly escalate. That means that the intervention doesn't last months or longer, and the US (or to a lesser extent, its allies) doesn't actually land troops. For various reasons that I might cover later, I think both outcomes are fairly unlikely (though hardly impossible). But if either of these conditions changes, my logic for supporting the war changes completely as well, because downside risks grow dramatically (American soldiers dying, major backlash in the Muslim world, dramatically higher costs, etc.). Right now, however, with no American feet on Libyan soil, it seems to me that the Pentagon and the administration always have the option of simply pulling up stakes if everything goes south. It wouldn't be pleasant, but the outcome wouldn't likely be tremendously worse than what could have happened otherwise, either.
*Update: here's one example I just ran across, from the Time Swampland blog:
Moreover, the rhetorical focus on the crazy things Gaddafi might do obscures the debate America should have before intervening: does the value of preventing possible war crimes against Libyans outweigh the risks to America's national security that come with intervening?It's not quite explicit, but when they say "risks to America's national security that come with intervening," they apparently mean stuff like al Qaeda exploiting "the power vacuum that will come with a weak or ousted Gaddafi." Does that mean if America ultimately decided that the power vacuum was worse for its national interests, we should actually consider helping Qaddafi? Again, where was Swampland when everyone was cheering for the rebels two weeks ago? What's changed?
Obama and his aides know they are taking a big risk. "It's a huge gamble," says the senior administration official. The administration knows, for example, that al Qaeda, which has active cells in Libya, will try to exploit the power vacuum that will come with a weak or ousted Gaddafi.