You are correct. Reductio ad hitlerum is a fellatious argument.
I don't think the argument is quite so simple.
The father of evolution's cousin Francis Galton, as well as R.A Fisher and Karl Pearson, founders of the very powerful eugenics movement, not to mention Julian Huxley, are not minor fringe cranks in early evolutionary philosophy. These men were well known, mainstream scientists. If Peter's or Paul's Christian cousins were discovered to have founded the Klan, then you might have a comparison. It's well documented too that Darwin himself was also a serious racist.
It seems entirely in line with evolution itself to hypothesize some groups of humans through genetic adaptation are more "advanced" than others...while other more isolated groups are being left behind. This sounds like a very logical rationale for racism to me.
Are the events of the first half of the 20th Century coming out of the most educated parts of central Europe, by the generation educated by such men, therefore just a coincidence?
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You do of course know what 'fellatious' means...
Funny how mis-placing a ‘t’ where a ‘c’ should be gives a whole new context to a statement.