> "We would essentially be the same person if we had been adopted at birth and raised in a different family.".

If you look at twins that are raised apart this is freakishly true. Twins raised apart have outcomes that are far closer than 2 unrelated kids raised together.

> And what about all the studies about the consequences of father absence?

If you look at children with an absent father vs children with a dead father you find that 80% of the effect disappears in the second group. And that still doesn't entirely eliminate the genetic component because genes influence behavior that can lead to death. This strongly suggests that sharing genes with a deadbeat dad is worse for you than not being raised by a father.