Only when scientists do it is it NOT a search for purity. when ignorant Nazis do it...well, we know the rest.
When scientists were doing it back in the 1800s it was all about racial purity. Otherwise where did all the oddball racial theories come from? I have no reason to think that it would be any different now. Human beings are sinful fallen creatures prone to the game of oneupmanship.
BTW, I'm not saying the research isn't legitimate or useful but the history of science is what it is.