How can one man supposedly be the cause of so much evil?

The theory of evolution is, like any other scientific theory, simply an attempt to understand how a part of the universe works based upon observation. No more, and no less. It was an explanation built around data and has been corroborated by more data as time went on.

Evolution has been pretty consistent with the workings of the little part of the universe that it describes, just like general relativity, quantum mechanics, electrodynamics, etc.

During the theory's existence, evolution has been derided and demonized by a very vocal opposition. As of late, this demonization has only increased. Terms like "Darwinists" and "Darwinism" are thrown around to make it seem as though mainstream biologists are following the cult of a single personality. (The current understanding of evolution, of course, is the culmination of the work of many biologists over many years.) In particular, Ray Comfort's recently-released abridged version of Origin of Species has an added introduction (written by Ray Comfort himself) that links Darwin to the most infamous atrocity of modern times: the Holocaust.

Evolution does not describe a human way of life just because it is based upon observations of life in nature. It does not tell people how to treat other people. "Social Darwinism" was a flimsy excuse used by those who supported the abuse of greater power (such as those who supported European imperialism) by trying to give their cruelty the legitimacy of science.

Ray Comfort is simply going the other way. He attempts to remove the legitimacy of evolution by tying it to those who used their power for cruelty. At the same time, he ignores the death and destruction people have inflicted onto other people for as long as history has been recorded.

Here's an analogy: consider a crime where a man murders a child. This evil act mirrors an action that happens in nature: adult male lions and bears often kill cubs. The murderer is the one who is responsible for the crime, not biologists who publish research articles on the behaviour of lions and bears. In the same way, how can evolution be blamed for the actions of people who can think for themselves?

Adolf Hitler was evil. Enough said.

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In the second season of Star Trek, there was an episode called "Who Mourns for Adonais?" in which Captain Kirk says to Lieutenant Palamas:

... we're the same. We share the same history, the same heritage, the same lives. We're tied together beyond any untying. Man or woman, it makes no difference. We're human. We couldn't escape from each other even if we wanted to. That's how you do it lieutenant, by remembering who and what you are: a bit of flesh and blood afloat in a universe without end. And the only thing that's truly yours is the rest of humanity.

There is a great diversity of people across the world, to the point where wars have been fought over these differences (and not just competition for scarce resources). Yet, from the scientific study of genetics, people across the globe really are not all that different from one another. We are one big family. That is enough reason for us to work together for a better future for all of us.

Peace and long life.