When thinking about the Western intervention in Libya, I think it's important to think about the particular situation in Libya, and not about the whole doctrine of "humanitarian interventionism" in general. I tend to think doctrines, policies, and ideologies tend to be a whole lot of bunk when talked about in the abstract, and I have no interest in wasting my time trying to defend one particular ideology in which I don't particularly believe. So, I want to confine my discussion more specifically to the Western intervention in Libya, and the particulars of that case.
I think it's important to think about the set of events that tipped this whole situation off to begin with, the initial uprising against Gadafi, and for that matter against Ben Ali and Mubarak and Assad, et al. Was the Arab Spring created by, or even sparked by, the West? I don't think so, and here is my reasoning.
Given how several of these leaders were solid pro-US authoritarian regimes, the realpolitik of the issues would argue otherwise. If Iran did not have its own problems with domestic pro-democracy agitation, it would fit their interests far more to promote popular agitation against those dictators than it would the interests of the United States. Further, the impetus behind these movements has only partially come from the hard-line Islamic sorts who would seem to be Iran's natural allies - were the whole Sunni/Shi'a split not a barrier to effective Iranian involvement to begin with.
Given that we are talking about generally pro-US authoritarian leaders here, who are not always terribly popular in, I think it is at least plausible to think that these movements were indigenous in nature.
In Tunisia and Egypt (who knows what's happening in Yemen), the indigenous movements seem to have succeeded without the need for significant outside support. Whether there was outside support, and how significant it was, is an arguable point - I have seen no convincing evidence that any US involvement with the pro-democracy movements was particularly strong or effective. But I could be wrong on this point. I really don't know.
Libya, in the person of Gadafi, had quite possibly the worst authoritarian dictator of all the Arab countries. Just look at him! As such, it would not at all be surprising if the Libyan people were, on average, more angry at heart at Gadafi than the peoples of the other Arab countries were at their dictators. Maybe anger isn't really comparable in that manner, and maybe it doesn't really matter. But I don't think it's very controversial to say that Gadafi was not terribly popular with a good number of his people, regardless of the international position on him.
Despite that, at the beginning of the year Libya was stable, selling oil to the West, and cooperating with the international community. There was no reason to support his ouster that there hadn't been since the 80's. I haven't heard anything to the contrary of this, but I suppose I could be wrong.
Then Tunisia happened, then Egypt, and then everywhere, including Libya. Again, new evidence notwithstanding, this seemed to be a real indigenous uprising. In Libya, the situation very quickly turned into a proper civil war, one half of the country versus the rest, well before the West did anything.
Maybe Western intervention was not a good idea. Maybe we should have let Gadafi crush the rebels. Maybe if we'd left the situation alone, the rebels could have gotten their act together on their own and beaten Gadafi, although I don't think it's unreasonable to say that the war would have gone on longer in that case.
But the West did not. It intervened with a fairly limited airstrike campaign. New evidence may contradict me, but I do not think a massive airwar of devastation was launched, nothing on the scale of the Iraq war. Nonetheless, bombing did take place, people were killed, and stuff was blown up. Partially because of that, the rebels got their act together fairly quickly, and now have beaten Gadafi.
Maybe this will turn out poorly. Maybe the rebels will fall out amongst themselves, and Libya will still have a long and protracted civil war. Maybe some radical group will take over, Bolshevik style, and impose a new crazy and insane government on Libya. Maybe they will muddle through, and cobble something together. At this point, we don't know.
Furthermore, whatever government emerges, it's not clear what sort of relationship with the West they will have. It is rather unlikely that the entire country will be turned over to profiteers, as in the wake of the Iraq war, simply because there will be too many local politicans, warlords, and whatnot who will insist on taking their cut and have the ability to do so. This may well be bad, but it probably won't be all that different than the division of spoils under Gadafi, where he personally pocketed everything. Should the locals put together a strong government and demand tougher terms, I really have trouble imagining the international community organizing ANOTHER civil war, or a proper invasion, to oust them. I suppose it's possible, it just doesn't seem likely.
All that said, I don't think "Just leave Libya alone" would have been substantially better for either the US or for Libya, as the country had already descended into chaos before the West did anything. The fighting, for now, has certainly ended more quickly than it would have if the rebels won the thing for themselves, and it is arguable if the West caused more damage with its bombing campaign, and the fighting this allowed, than Gadafi would have employed to subdue his own people. Just before the bombing campaign began, Gadafi was using heavy artillery and rockets to bombard rebel cities - in sustained fighting, he could well have destroyed far more of his own country, and killed more of his own people, than the West managed. This is a truly hypothetical what-if that can never be answered properly. But it seems truly debatable.
Further, assume Gadafi won on his own, bombing the rebels into submission. He already ran the state for his own personal benefit, and it seems rather unlikely that he would spring for a massive re-building project in the rebel areas. Time will tell if that dark prospect will look good in comparison to reality - but I find it unlikely. Again, it's a false comparison to compare old Libya, before the Arab Spring, to whatever comes now, because that old Libya had already disappeared before the West did anything.
And to shill for Western capitalism, it's quite possible that Western companies could manage Libya's oil assets and exports far more effectively than whatever was in place before. Sure, they profit insanely from it, when they are allowed to. But that is a political choice, one that the government will allow or not. And again, Gadafi ran the country for his own personal benefit, and it's hard to get much worse than that.
Further, that involvement and participation could well make a variety of other large investment projects more feasible, in a shorter time-frame - the trans-African railway I heard DoDo mention, or Desertec, or whatever. Further, North Africa has been cut up into tiny, isolated chunks since not long after independence. Who knows what good will come from having Tunisia, Libya, and Egypt open to inter-African trade and travel? That area had been interconnected for thousands of years, and its recent isolation is a bizarre abberation from that trend. Libya has usually been an appendage of Egypt, and anything that helps re-build ties between the two countries is probably a good thing.
So there, I've defended the acts of the Western powers in Libya. Discuss.