I do not entirely disagree with the premise of your first argument. Injecting people of different culture, especially by manipulation and politicking, into another is more likely than not to create a bad situation.

Diversity of thought can be a bad thing if TRUTH is not honored. If we must pretend a man is a woman because he thinks he is, then diversity of thought is bad because we are forced to accept a non-truth (A LIE) for sake of thought diversity or the lie that diversity of thought is more virtuous than the truth.

I argue that an interracial couple mating and reproducing likely pulls from a more diverse selection of genes, giving more options for dominant ones to prevail.

Whereas two homogeneous mates from same society dating back generations have more similar genes, giving more chance to poor choices between two recessive genes or not enough of a diverse pool of dominant genes to pull from.

I know this is going to make the guys who pretend they are pure blood white mad.

We see what generations of inbreeding do. Look at the jews. They look like disfigured goblins.