If we are a nation of laws, and expect other nations to abide by international law, then we cannot simply disregard international law, or its processes, without becoming a rogue state ourselves.
A moral stand is a good thing. However, people have committed horrible atrocities in the name of morality, when they are unchecked by respect for the law or other limiting institutions. Emotion is a powerful thing, but when you let it control your decisions as a nation, you become a bully, getting your way because you can beat up all the other kids on the block.
It is the fact that we knowingly and willingly limit our power and our ability to respond to situations by bowing to the strictures and conventions of international law that separates us from madmen and tyrants like Kadhafi.
