Do you feel that by doing so you're being judgmental about your fellow gamers who do feel it's just a game? There's certainly a degree of it all through this thread.
Right now, it looks to me like you're expressing some ambivalence. You aren't going to stop so any problematic aspect of doing so, any creepiness/juvenileness you see, is only of limited value in changing your own behavior. Yet you suggested a degree of judgement as well. Do you really think slaughtering the goblins under the justification that it's a game is problematic? Under what justification is it not problematic? Is this even something worthy of the philosophical discussion?