U.N. and NATO as war referee?

I get that the U.N. should prevent war crimes whenever possible. But what exactly are we all doing in Libya? We seem to be enforcing a pretty arbitrary set of rules. 

"You can have your war, but you can't use airplanes. Also, if you are one side of the confict, you might not want to use tanks."

We're not arming or supplying either side, so really, what, what are we doing?