I think we've had enough of these charades. It is all a cover to spread hatred of those considered less worthy, and a means to promote an anti-Catholic concept by disguising it as Catholic, and by layering on one false accusation after another against mixed ethnic groups.
There is no master race, no superior race, no such thing as pure blood. It is all a deception, and you have bought into it. Christ is the shepherd and we are all His sheep. In this context, it is pointless to argue on which sheep are superior.
The Church has not condemned, prohibited or restricted mixed ethnicities. If you have a problem, that is because you hold your false, humanist-inspired notions above the teaching of the Church.