First off, the alignment system right now is pointless. A single hat that changes based on your alignment? Cool, something totally pointless. Add areas like gun shops and hangouts that have alignment requirements you must meet to enter. Hold your "People will just pk a little and change their alignment to get in" for a second there. Now, remove alignment changing from pking altogether. Why? Hold on, I'll get to that.
Okay, so, add mini-quests people can do that reward with a little cash and a small alignment change, but only every 1/2 hour to 24 hours (depending on effort/reward ratio). Now see? People wouldn't be able to change alignment so easily. Make sense?