It's because of...well, all the negative connotation. The studies now are more of a literal approach to improvement, rather than what it became. Charles thought of the Nazis use of that word in the things that they did. His study in genetics was not without touching on what Eugenics was and what it has become. Of course, he was always more interested in Mutants, a natural evolution, rat her than the forced one that Eugenics implied.

I was born in '32. I was a little young for the war, Charles smiled a little. Did you? he asked. Sure, he could find out, if he had wanted, he was sure. He remembered how mad it made Erik when he dove into the memories like that.