We should RP as if there were specific laws. They have not been disclosed to testers now, but they are in the agenda of the devs. Yes, it's true that not everyone will take that into account when they choose to commit RP crimes, yet when we RP around certain limits (like having a set of laws), I particularly find it to be a better and richer RP. As I said in a previous post, evil aligned characters should take the existence of the laws as part of their RP because they are going to break them, that makes their characters true outlaws, thieves, bandits, murderers... The notion of "murder", for instance, is different from "killing" because the first is defined as a crime, while the latter just an action that is abstracted from the concept of society and its consequences.
Can you drag a monster in town and get away with it? Yes. Can you RP that you poison someone in front of 20 people and then act like nothing happened when they know you just committed murder? Yes. Should you? Should the 20 people just let go? Well, that depends on how serious the murderer takes his actions. Both parts need to see the crimes as something they have to consider seriously.
Maybe I'm being too serious about it but I still think we can't just turn a blind eye in these situations because we're missing a good opportunity for interesting RP. I think that evil characters are defined by their evil actions. If these actions have no consequence, there's no real evil, thus no real good.