You have the timeline backwards if I'm reading your post correctly. You seem to be saying that racial discrimination on the basis of scientific "evidence" was only around for a few decades and then self-corrected.I feel like I'm having to repeat myself here. For all of human history, a million years or so, we've had a natural fear of 'others' that has led us to enslave and kill each other. For all of recorded history we've been making up justifications for this behavior. Initially we tried to carry over those ideas to science, but because of the self-correcting nature of science it only took a few decades to figure out that these ideas were completely wrong. That's incredible, no other idea in the history of the human species has been able to accomplish any sort of change like that so rapidly.
To argue that it was science that 'essentially led to the holocaust' is to be willfully ignorant of the facts. It was ignorance and hatred that led to the holocaust. There was never any real evidence for racial supremacy, people just wanted to dress up a deeply held belief in scientific terms. If you're going to argue that science caused the holocaust you might as well argue that it was science that led the Catholic Church to burn poor Bruno alive. Their ignorant view of the universe was widely believed by scholars of the time, after all.
Scientific "evidence" for racial discrimination was used for roughly 150 years and it's only been in the past few decades that genetic information has been used to undermine that position.