There is certainly something like "senseless race mixing". Nietzsche was for something like mixing prussian officers with rich jewish girls. The first lack wealth and the second virtues. And yet, the offspring would be something new in the society. How would they take part in it? So, I guess only if there is a place for them, then it makes sense to bring them together. In democracy nobody can take a solid place within the society and thus every mixing becomes senseless - for the sake of "equality".