Many critics of the Libyan intervention make their case based on moral consistency: We didn't intervene in Congo or Zimbabwe, so why are we intervening here?

My former colleague Peter Beinart, writing at The Daily Beast, answers:

The consistency argument, it’s important to understand, has nothing to do with Congo and Zimbabwe. Most of the people who invoke those ill-fated countries showed no interest in them before the Libya debate and will go back to ignoring them once Libya is off the front page. Ask someone who demands moral consistency in humanitarian war how exactly they propose to intervene in Congo and you will quickly realize that the call for moral consistency is actually a call for immoral consistency. The point of invoking the horrors of Congo is not to convince the US to act to stop the horrors of Congo; it is to ensure that, out of respect for the raped, murdered and maimed in Central Africa, we allow innocents to be raped, murdered and maimed in North Africa as well. The Congolese, presumably, will find it comforting to know that the great powers are as just as indifferent to savagery in other lands as they are to the savagery in theirs.
There is a serious argument against humanitarian intervention. It starts with the belief that international affairs is by nature tragic. Terrible things happen in distant societies but we do not really understand them, and so our efforts at amelioration either prove futile or actually make things worse. We think that because our motives are pure we can violate the norms of sovereignty that we guard jealously when it comes to our own affairs, but in so doing we open—or reopen—the door to a predatory imperialism that can do even greater harm. And finally, by spending money on distant lands we bankrupt our own.
What unites these arguments is a belief that foreign policy must be Hippocratic: First, do no harm. But the advocates of moral consistency cannot stomach this moral minimalism so they cloak it in moral maximalism: Rather than arguing against humanitarian war anywhere, they argue for it everywhere, which is a less honest way of saying the same thing.