This kind of agreement is incredibly common in families with histories of mental illness, drug abuse, criminality, and other major issues. I know dozens of people who have all agreed to never have children for this and various other reasons, and half of them are in long-term, committed relationships or married.

In at least one instance, I’ve seen the DNA analysis and the family tree. This particular family has a known gene for heightened intelligence (related to Scandinavian heritage, it’s well known, you can look it up), and their family has an uncanny predilection towards careers involving mathematics stretching back over a century. I’ve seen this ability with my own eyes. It’s uncanny and bordering on savantism.

The problem is, in as much as their genetics gives them a head start towards math, it is also heavily weighted towards certain forms of sociopathy/psychopathy and criminality; their family tree is heavy with addictive disorders, extreme religiosity, murder, substance abuse, and mental illness. The youngest member of their family is currently in prison as a recidivist. He’s only 27.

I don’t see it as "fucked up" at all for these people to stop having children; they are trying to be socially responsible for their progeny, some of which may have a genetic predisposition towards bad behavior. The philosophy of movements like antinatalism and childfree are rooted in these ideas and seek to make the world better with less humans.