In terms of playing, I can't recall ever really playing differently live or online in terms of feeling bad towards raising or stealing or whatever.
I thought you actually meant by insulting players, slow rolling etc because I was going to say it's because you are safe behind a monitor so it gives you that extra "bravery" of being able to insult someone. It probably doesn't come down to you feeling rude or caring about their feelings, it's simply because in live games you will likely be scared of any confrontation where as online, this wont happen so that's why you find it easy. You usually find when someone comments on your play, insults you online or slow rolls or whatever; that most of the time - these guys wouldn't say or do, or say anything to anyone in the real world.
Keyboard warriors I think they are called.