That doesn't justify his actions at all, you choose if how you grow up fully influences you. He choose to be abusive at most... it doesn't matter if he "didn't mean for it to happen" he still let it happened even when he was that he was hurting Jooin. Just because you weren't loved as a child doesn't mean you don't know how to, before meeting Jooin once again he had the opportunity to learn again.

Ya'll really complain that Yahwi needs to be nicer but when someone like Cain comes a long and he's nice it's somehow suspicious?
Like you're basically saying, "Oh he's to nice that's suspicious... but he's to mean he needs to be nice." Like just because someone is nice doesn't mean their suspicious.