I am new here, but I have an idea that might go a long way to alieviating fear about PKing.
How about something as simple as alignment. Everyone starts with a neutral alignment, doing good things(quests) tilts it toward good and doing bad things(evil quests, pk\'ing, etc) tilts it toward evil.
The color of your name can show if your good, evil or neutral and to what degree. Good towns wont let evil in, and there can be evil towns where the guards kill any good char who come near.
If you kill anyone who isnt evil, it shifts your alignment toward evil. That gives you a large incentive not to kill, since once your evil everyone else can maul you at will with no consequences for them. But it also leaves the door open for you to play an evil char if you want to.
The key is consequences, if being an rpk\'er means that within 5 kills I cant go into town anymore I\'m probably going to find another line of work. Unless I go off with my buddies and start our own evil town, from which we raid the good town and they send ppl over to raid us etc. It keeps the crafter/social types mostly safe within the walls of their own city, unless a particularly large or powerful group of evil char\'s come into town.