I don't know why people can't get their heads around the idea that politicians have to be pragmatic towards foreign policy. Some assholes can be assholes with more impunity than others. They have more strategic geopolitical capital to burn, the countries who could intervene would have more to lose, and / or - they simply weigh the strategic odds of long term failure as against their national interests.
Doing nothing would have halted the democratic surge in Africa and the Middle East -- tyrants everywhere would have seen that they could respond to popular uprising with extermination. They would have been shown that they could get away with it... that the US and chief European powers are too 'overstretched' to stand in their way. Gadaffi had no cards to play to protect him from the consequences of his actions. No justification, no allies, no hope. Even his fellow African tyrants have not bothered to cry crocodile tears for him. He is a known tyrant, with a proven history of belligerence and links to terrorism. Having watched Mubarak try the strong-man card and fail, he went even more hardcore in his violent response, and openly stated on the world stage that he was going to go house to house cleansing his country of his popular political opposition. His actions resulted in foreign ex-pats fleeing into exile, the destruction of what progress Libya had made in integrating into the international community, and turbulance in the oil markets - as Libya produces 2% of the world's oil. He was not only threatening the peaceful protest movement sweeping the middle east, he was threatening thousands of innocent lives. The UN did the right thing for once and managed to act before it was way too late.
We're all too quick to criticise our own leaders -- sometimes, cunts like Gadaffi bring things like this on themselves!
The toil and cost of unpopular and incorrectly justified wars like Iraq has clearly made us weary of getting involved in further conflict - but the world has to be strong, but pragmatic. It cannot turn always turn a blind eye and appease in moments like these.