I can't remember the specifics, but it's something like women over 40 have just as much chance of producing a birth defect as incest. The real problem comes when incest is repeated for multiple generations, like royal families did. But that's extremely unlikely without the "royal blood" concept anymore.
This ignores the reality of incest having a far higher chance than non-incestual pregancies of producing a birth defect.
But I agree, we don't do eugenics on people with Down's or autism, so that justification here is bullshit.
I can't remember the specifics, but it's something like women over 40 have just as much chance of producing a birth defect as incest. The real problem comes when incest is repeated for multiple generations, like royal families did. But that's extremely unlikely without the "royal blood" concept anymore.