The thief primarily has one purpose: to steal and accumulate gold and treasure. Making your thief into some sort of assassin or pvp killer makes absolutely no sense at all. 4 or 5 of your skills are devoted to stealing and stealth... that leaves 2 or 3 skills at best to devote to something else... What sort of effective PvP character can you really be? Or you can water down your thief, take away his essential skills and then he is not going to be very effective at stealing. You can't be all things in life.. you can't be a rock star and an accountant... You have to choose!