I just started my Thief/assassin so I can do the TG, DB and deadric quests. And I might search for the masks also.
My other characters have all gone the moral ground, this char is going to be the opposite, I am hoping to be able to get into the role just as much for her as for the others. I haven't fleshed out her back story yet. But I Only just started she's at lvl 9..
I'd bet that, thief and assassin she may be, she will not actually be evil. My theory is that by the time a player has invested the energy and, let's be honest, emotion in creating a back-story and played the character for a while they can only carry on with the game if they can empathise with their creation. Creating a character that is too far from the player's own values leads to what the Original Poster has experienced.
Any psychology graduate looking for a subject for their masters, or doctoral, thesis could do a lot worse than how people play computer games. Given that the industry is now worth £25 billion a year (and still growing), whole careers can be built on the back of it.
[Edited because of typos]