Your question is really more sociological than genetic, because some cultures and sub-cultures have a bias known as positive assortative mating - mating of like with like. However, in any environment where people of differerent races freely interect there will always be interracial mating. In many societies this is not the case however, in fact most non-Western societies are still very racially homogenous. As globalisation increases I imagine this will gradually change but until then the idea of race will always exist, particularly in nationalistic societies with low immigration.
As far as the scientific basis for race, I will play devil's advocate and say that there is in fact a scientific distinction between races. Haplotypes in DNA are grouped by race, but evidence for any significant racial differences in the DNA other than obvious morphological traits and non-coding hypervariable regions is scant. There is no such thing as a pure race and variation of individual factors within a population is higher than between populations. This does not mean that correlation between factors cannot be used for ethnic grouping.
