To prevent a moral dilemma, think of this:
If you want to play good, you shouldn't kill Plox.
If you want to play evil:
Evil means egocentric, right? If you want experience for you and do not care about the rest, it's evil, then. If you get experence for sparing Plox, you've just commited a very evil act <img src="/ubbthreads/images/graemlins/winkwink.gif" alt="" />.