Stephen M. Walt in Foreign Policy:
With the U.S. and NATO's thumb firmly on the scale, the balance of power in Libya seems to be shifting steadily toward the rebel forces. That's bad news for the Qaddafi family, though their lack of attractive alternatives to fighting on makes it unlikely that they will simply surrender. This outcome is also not that surprising, as the Libyan military was never a first-class fighting force and it was not going to have real trouble standing up to the rebel forces once they started getting lots of outside help. The danger, however, is that the rebel forces will not be able to consolidate control over the entire country without a lot more fighting, including the sort of nasty urban warfare that can get lots of civilians killed.
As with the invasion of Iraq, in short, the issue wasn't whether the West could eventually accomplish “regime change” if it tried. Rather, the key questions revolved around whether it was in our overall interest to do so and whether the benefits would be worth the costs. In the Iraqi case, it is obvious to anyone who isn't a diehard neocon or committed Bush loyalist that the (dubious) benefits of that invasion weren't worth the enormous price tag. There were no WMD and no links between Saddam and al Qaeda, and the war has cost over a trillion dollars (possibly a lot more). Tens of thousands of people died (including some 4500 Americans), and millions of refugees had to flee their homes. And for what? Mostly, a significant improvement in Iran's influence and strategic position.
In the Libyan case, same basic question. Hardly anyone thinks the Qaddafi family deserves to run Libya, and few if any will mourn their departure. But assuming the rebels win, will the benefits of regime change be worth the costs?