At what point do we draw the line?
Dr. Joseph Mengele performed barbaric medical experiments on prisoners as did the Japanese doctors in Unit 731. Do we use the medical knowledge gained from those experiments (and it appears we did for Unit 731), or do we refuse to accept the work of human monsters?
Did von Braun have a hand in on the terrible concentration camp operations in the V-2 factory? He denied it, and lacking evidence to the contrary, I'll take him at his word. However, if he did participate in running those camps, then he was a war criminal.