Your notion that it is equally absurd to blame evil actions of others to Darwin and Christ doesn’t quite hold up.
I agree that Christ has had many horrible, evil things done in His name - but, all those acts were contrary to His teachings. What evil act by others can you honestly attribute to one of His sayings or teachings from the New Testament?
Darwin, on the other hand, while he may not have been a complete believer in eugenics, taught ideas about human origins that logically and ultimately lead one to the beliefs held by eugenic’s ideologists. Human beings are just flukes of nature with no special claim over any other fluke or flukes of nature. Moral objections to eugenics are nonsensical if there is no God.
I think you may be putting some words in Darwin’s mouth. I don’t think he was promoting the idea that there was no God.
From a purely Darwinian perspective there’s a strong practical objection to eugenics. Evolution is the result of natural processes, we can only guess as to what made one species better than another and subsequently more deserving of survival. Eugenics is an attempt to override a natural process, declaring with our limited knowledge which section of humanity is better and more deserving of survival, the problem is the eugenicists might be wrong. The proper Darwinian approach to improving humanity is a species is to not, just do your thing and let nature take it’s course, eugenicists pervert the concept for their own twitsted purpose.