Repoputating with inferior genes is already well underway:

Every 20 years or so, since the civil war, the USA (and Europe) has a war. Only the BEST young men are allowed to serve and die. Anyone inferior with a prison record or handicap remains behind to marry. Every generation you wipe out your best and brightest...With us, the weak were not able to marry. If a man didnt have a child yet, others were sent to fight until that warrior had a child by one of his wives...(that we survived at all is a miracle, altogether.)