I don't remember what reasons those are, but they're probably bad and should not be encouraged. This is a roleplaying game, not a number maximizing game. If you have the choice between resolving a situation peacefully or violently, those each have consequences.
I vote in favor of setting NPC XP to zero if you make the choice to resolve a situation through peaceful methods and succeed. That is the consequence you get for making a choice to be peaceful. You should not be rewarded for then doing the opposite.
Right there with ya, it just doesn't bother me at all if it is possible because I wouldn't do it anyways, at least not intentionally. I think your solution is the best and probably really easy to implement too.
