The justification of "I do it because I can" is quite frankly a childish sociopathic attitude. Of course, the true nature of these kids come out in online games where they can behave exactly how they really want to with 100% anonymity and 0% accountability.
Yes it's a pvp server, it can and will happen. Doesn't make it any more pathethic/childish and doesn't make his gripe and less valid. It's petty and childish whatever way you try to justify it
Granted complaining about it won't change anything, but he's perfectly entitle to