Godwin's law doesn't actually comment on the aptness of the comparison. It just says it is so frequent that it loses all effectivness.
The bigger logical error is that it doesn't even matter if Darwin was really Hitler himself. Scientific theories stand or fall on their logical merits, not on how human agents apply them.
This thread will end up disproving nothing about the theory of evolution, since it is off in an illogical vein.
Not so much illogical as fallacious premises and clearly propagandistic approaches.
I consider arguments from (presumed) consequences and guilt by association to be not so much logical fallacies as straight propaganda.
"Scientific theories stand or fall on their logical merits, not on how human agents apply them."
Then why strain credulity, denying the (perhaps unforeseen) societal consequences of certain scientific theories? Everything I've read points to science having run, screaming, away from eugenics, once all the many Nazi atrocities began coming to light. Did eugenics fall on logical merit, or did the application of eugenics, taken to its logical extreme, create societal consequences so utterly inhuman, as to place eugenics into some special, pariah-class memory hole, for the scientific endeavors you'd rather forget?