That's one of my only beefs with the IQ side of the alt right. "Regression to the mean" shouldn't be some kind of epiphany, it's common sense. If two super smart people were guaranteed to produce even smarter offspring then we would have human supercomputer Mentats by now. That doesn't mean it's bad for smart people to marry, but the eugenic benefits will usually happen not at the level of the individual, but the population.