Isn't it more the question about consistency?
If goblins can be killed so should humans and elves which IMHO is much better (so basically what FO2 did, rather than F3).
Although, if no other way (which probably is the case in order to please SJ warriors), none should be allowed to be killed as a compromise. I guess what I'm trying to say there should be all of them or none of them allowed, for the sake of consistency.