Originally Posted by Ronin4hire
Race is nothing but a social construct. It has no biological basis.
Breeding outside your own race would not result in any lack of "purity" as you imply.
Your first point is, in my opinion, true, but not all scientists would agree. In truth, words such as "race" and "ethnic group" are quite ambiguous in the first place. But it is certainly true that "blacks" and "white" are social construct and have little to do with race.
The second point is wrong, if you mate with someone of another ethnic group, your kid will be less pure. If you want purity, mate with your sister/brother/cousin. Of course, your child is much more likely to be disabled. In genetics "pure" and "weak" are synonyms. We even have a word; heterosis (or hybrid vigor) to explain why kids of genetically-distant individuals are stronger.