I think you’re close to the root of it. The need for a biological legacy is strong no matter any affiliations. Having “non-conforming” children threatens that legacy.
For the groups that inflate this drive, that’s all there is. That’s the only purpose. No “we as a species”.
For the rest of us it might be a little disappointing at the prospect of no grandchildren. But we know that it’s ultimately not our decision. And the same outcome could happen regardless of any “conformity”.
Reminds me of the North Carolina Black Republicans.