Lol
But I don't quite agree, I mean even irl you'd at least subconciously shy from harming a friend even if you had to.
And in OP there's an entire power system based on willpower, we've been seeing mental nerfs since Water 7.
And trust me, if it wasn't mental nerfs it'd be some other BS like "Ki control" or " He lives in a world of cardboard and always holds back in even in dire situations for some reason".