on People born of rape

I was watching a show with my parents recently, where a guy in highschool (I think) tried to kill a man because he raped the kid's mother so long ago. The mother didn't press charges, and was apparently just trying to forget the whole thing happened. eventually he found out after questioning who his father was, and afterwards starts plotting murder.

I asked my parents why they think someone would do something like that. My dad said that if the mother isn't happy, no one is happy. In a tone of voice that made me think he didn't want to talk any more about it.

That doesn't really make sense to me, though. The mother is reasonably happy. Nothing good would come out of killing the guy because there was no evidence that the man was a repeat offender. He said himself that it was a mistake and he was sorry about it.

The main thing I'm curious about is why would someone be so furious at a guy for bringing them into the world? Sure it was illegal, but I didn't have reason to believe his life was so crappy. Even if it was, suicide would be better than murder.

You might be able to just say he wasn't thinking rationally, and that's just that. Or maybe I'm thinking too deeply about something that's supposed to make the attempted murderer sympathetic.

Why would a person be violently angry at someone when that someone gave them life, even if it was through illegal means? I could understand if it was about other things, like if the guy was still after his mother or something like that, or if he was still raping other people. But the kid was angry at a guy that raped someone, that caused him to be born. Personally I think I'd cut the guy some slack if my life wasn't too bad.