1) President Obama is the commander-in-chief, and unless he's starting an actual war, he doesn't need Congress' approval.
2) The United Nations is nowhere near as powerful as you seem to think in itself. Its power stems from the fact that pretty much all of the most powerful countries in the world are sitting on its Security Council and willing to enforce its resolutions. It has no aircraft or missiles with which to implement a no-fly zone, and it doesn't even really have troops.
3) Yes, there are lots of dictators out there in the world. At present, Gaddafi is by far the worst. We can't go around deposing every dictator in the world, because we would destabilise dozens of countries. It's only when they begin to massacre their people that we should get involved.
4) Libya has a stronger opposition movement than any other country currently staging an uprising. The rebels can actually defeat Gaddafi, with Western help.
5) Oil prices will fall if the chaos in the region subsides.
6) Gaddafi has shown that he is completely unwilling to stand down. Everyone in his country not in his payroll hates him, and yet he continues to claim that he is divine leader.
I would say that's enough reason, but I'm sure there's more.
(Former) Lead Moderator and (Eternal) VGC Detective 
