If nothing else, because evolution doesn't have beliefs. As Dawkins says in the letter that kicks off this thread,
"natural selection is a scientific theory about the way evolution works in fact. It is either true or it is not, and whether or not we like it politically or morally is irrelevant. Scientific theories are not prescriptions for how we should behave."This is something I've been wondering about recently. Let's say you're right--Hitler was a big fan of Darwin and really thought he was acting in accordance with some kind of evolutionary principles. So what? What does that have to do with whether the theory is correct or not? People have used the Theory of Relativity to argue that everything is subjective, that there is no objective reality or morality--is that an argument against the validity of the theory? Charles Manson thought a song about a playground slide was a coded message about race war--does that mean I'm supposed to stop listening to the Beatles?
Darwin’s hypothesis removes all moral restraint.
When you remove all moral restraint, you get people like Hitler, Harris and Klebold.
Evolution as a belief, should not be rejected because it has such admirers, but because it promotes them.
You should be aware that Darwin’s hypothesis cannot be ‘incorrect’ because it is based on philosophical assumptions, which cannot be disproved.
Something that is held to be true, but cannot be disproved, is not empirical science.
A belief is what you end up with.