That’s actually not true. You see if both parents have similar genes then that actually increases the chances of them getting a genetic disorder, not decreasing. I mean, lets look at recessive genes; if both parents are carriers of the same illness, you have a 2 in 4 chance that your children will also carry the gene and a 1 in 4 chance that the child will be affected. Sickle celled anemia (a disease that black people are most vulnerable to) and cystic fibrosis (a disease that white people are most vulnerable to) are both autosomal recessive conditions. If both the parents have very different genes, they are more heterozygous and therefore less likely to inherit these diseases. What you are basically trying to say is that inbreeding is better than genetic diversity. That just boggles my mind, honestly.
And before you say “well, they will still carry both these diseases”, well not necessarily. If one parent is a carrier and one is not, you have a 50% chance that your child is going to be a carrier and 50% chance that your child is going to be completely unaffected. Also, there is a 0% chance that your child will have the disease. And lets say that, in the tragic event that one parent has cystic fibrosis and another parent has sickle celled anemia, the child is still much less likely to get either illness if either parent doesn’t have any traits of the other disease. It still decreases the risk, which is very beneficial to humanity.
As for your thing about the child facing prejudice, well it’s true that it happens but that’s a social construct, i.e something we can fix so your argument still falls flat.
By the way, if any biologists have seen any issues with what I’ve written then please correct me.