I highly doubt it. If that claim is put forward I'd be highly suspicious that the person in question wasn't abused in some way. A genetic study was done and the conclusion was there is no gay gene, homosexuality is the product of nurture not nature.

Depends on what you mean about "good nuclear families". I mean, much of this isn't scientific (because they won't research it), but even if there's no overt abuse, you can usually find the reason. The mostly "good" family (in social work/psychology known as "good enough" parenting), where there's two sons: one's the athlete, all-star, coordinated, etc., and one is not. Which one does dad pay more attention to, and give more esteem to? If the other one feels rejected by dad, sometimes that one ends up gay. But not always.

Yes but that contradicts his narrative so he'll dismiss the outliers. It's easier to live life with a simplified viewpoint because constantly challenging yourself is draining and disorienting.