I feel sorry for Touya's past, but he did not have to become a villain much less a mass murderer.
Endeavor was truly a crap father. Rei tried, but not hard enough, she should have forced Endeavor to acknowledge his son, and to come up with a new plan rather that abandonment!
Touya could have still went to UA, and maybe the schools Development Studio could have come up with a costume that prevented Touya from burning so much. Yeah, give up on surpassing All Might, but he still could have become a Hero!
The kids were just kids, I dunno why they are blaming themselves. Shoto is the most innocent, yet most of Touya hate is directed toward him.