Exp should not represent if you are a good or evil person, but how much effort you put into doing something. At current state it is hardl given, easy fights often offer more exp than some of the hard ones, for example slaughtering Silent Monks.
Also I guess at current state, being good isn't rewarded enough, because being good is pretty always the harder way. But being good is also hard to repay. For some the challenge of being good is some kind of reward. Hard to say, on the other hand you could always offer the option of refusing a real reward. Perhaps some Karma-Mechanic would be necessary for appropiate treatment of both ways.
