I think it's the fact that you're doing bad things like stealing. Even if they're bad you shouldn't steal.
but if you're killing "enemies", don't their items become "fair game"? I mean, it's not stealing if you loot a raider's shack in Fallout 3.
They should make it so that if the item belongs to a faction that is hostile with you, the item shouldn't count as stealing. or at the very worst, just count as a reputation hit, not karma. This would change if you later became friendly with the faction. Though, they should also make it so that after a certain amount of negative reputation, you pass a point of no return, wherein for the rest of the characters game, that faction will be hostile with them. that way you couldn't just get unfriendly just to get some good loot, then play the "sorry" game and get friendly again like in Fallout 3.