I think as far as you can attribute the assholery to the parental home, it’s pretty much a bell curve distribution. Most people turn out well most of the time. And the edge cases just stand out more in our perception.

My initial post wasn’t meant to be the definitive comment on the subject. We mustn’t forget that it isn’t just the parents that have a hand in this. The environment where you grew up has an influence as well. And it is my observation that a culture that rewards individual achievements more than any effort towards the collective good will naturally create more assholes.