First, it is only a smear if it is not true. Weickart supports his assertion with numerous references, his assertion is well documented. Second, it is not intended to be scientific, but a historical link from one event, Darwinism, to another, the Holocaust.
No one is saying Darwin was a Nazi, they are saying that his theory had consequences.
Okay, explain why his Theory hasn’t resulted in a world dominatied by Nazis.
His theory is the most widely accepted theory for the species.
Was it a one-time thingie? If so, why?