Gaddafi claimed he would implement the UN-mandated ceasefire but never did, and instead blew smoke at the rebels, promising terrible vengeance. War crimes against civilians were a given tactic of his (he used civilian hospitals as shields for his troops). He was the primary obstacle to peace, and like Milosevic during the Kosovo intervention, he and his regime needed to be whipped into submission. At least Slobo was smart enough to eventually give up and go with the ICTY; Gaddafi probably believed he had taken the right course of action right up until he died.
Also, I'm not sure why you place so much stock in Russian and Chinese opinion on the Libya. First, they're at least as driven by economic and imperial interests as we are, if not much more. Second, we factor international law into our decisions - Russia cited a treaty and "coalition" (or council; I forget what it was called at the moment) that they had previously bullied Georgia into through their Ossetian puppet rebels and in which they unfairly outnumbered Georgia by 3:1 to justify their occupation and invasion of a sovereign nation. In any case, Georgia had no hope of taking their case to the Russian-dominated Security Council. When they had the audacity to reassert their territorial integrity by force in response to Ossetian militia firing upon them, Putin invaded unilaterally and bombed Tbilisi until Georgia couldn't fight anymore. Did the Russians at any point even ask the United Nations for permission to do this? They did not, and they wouldn't because they're the ones who truly bend international law to suit imperial designs, not us. Similarly, China refuses to let the United Nations deal with North Korea, and they simply declared their possession over islands that they haven't occupied since the Qing Dynasty because of the presence of resources (oil?) around those islands.
So they really have no right to be lecturing us about obeying international law, and their expansionist hypocrisy should not be taken as a legitimate opinion when we decide our foreign policy.