Bring back Dishonorable Kills, obviously, with some penalty attached to it. Sure, some won't care, but some will, which will certainly help the problem.
Oh and.
Don't like PvP, don't play on a PvP server. Nowhere in the server description does it say that all PvP on a PvP server is consensual, balanced, fair, enjoyable, fun, friendly etc etc. Get used to it. People are dicks.