This is something I thought I'd never see. In the comics, Shane died a long time ago. On the show Shane lives and is now causing a rift between the group not like the books. I, for one, seems to be the very few who have sided with Shane.
Shane is a functioning psychopath. He may be effective, and may know what he's doing overall in terms of survival, but he has lost his moral compass if he ever indeed had one.
He's a hot head with rage issues and an overly inflated ego. He's a bully. The only thing that matters to him is his own survival.