From what I can tell, the folks at PETA are, for the most part, small powerless people who want to feel important. In order to feel important, they begin to see themselves as the ultimate arbiters of morality in the animal world.
From there, it is only a small step to believing you are a God; the only proper entity to decide who -- and what -- gets to live and die. The law does not matter, social norms do not mater, and rules and regulations do not matter. Those things are for mere mortals. You are a God.
If you think this sounds a bit like a cult, you are not the first to notice.
If you think this type of thinking is not too far removed from that embraced by abortion-clinic bombers, 9-11 jet liner jockies, and animal-liberation lunatics, you are not the first to notice.
But, of course, there is an alternative. Author Nathan Winograd thinks he see something else going on with PETA: what he calls, Munchausen by PETA. Read the whole thing.