I don't know why this is such a hard concept.
Darwin came up with certain ideas.
Others later distorted and misused his ideas. One group that did this was the Nazis.
This does not make Darwin a proto-Nazi, but it is not possible to disclaim the intellectual line of descent.
I have pointed out in other posts that Marxism and Communism are in a very real sense Christian heresies. IOW, misuses of the teachings of Christ and his followers. This doesn't seem to have upset any of the Christians on this thread. It is generally recognized as true.
Why cannot believers in evolution recognize that this theory was misused by the Nazis and as a result some very bad things happened? If this it true it provides no evidence one way or the other as to the truth of the theory, it is only another example of the human ability to misuse anything.
Who doesn't recognize it? I don't know a single evo freeper who denies it. We're just very sick of people brining it up, because it's not a valid argument against evolution. It's a classic example of the guilt by association fallacy.
If Darwin is somehow responsible for Hitler, then Jesus is also responsible for those who have murdered in his name. Both assertions are stupid.