I suppose one need not be an atheist to believe the scientific facts which support Darwinian evolution. After all, no less a religious entity as the Roman Catholic Church "allows for the possibility that man’s body developed from previous biological forms", and many Protestant denominations either allow for or outright teach that mankind evolved from "previous biological forms," a position those churches are forced into by science.
Science has come a long way since Darwin's discovery and his publishing of On the Origin of Species in 1859. This is a blog, not a book, so let me just summarize the definition of the modern theory of evolution by quoting Dr. Jerry Coyne directly from his wonderful book, Why Evolution is True: "Life on earth evolved gradually beginning with one primitive species - perhaps a self-replicating molecule - that lived more than 3.5 billion years ago; it then branched out over time, throwing off many new and diverse species; and the mechanism for most (but not all) of evolutionary change is natural selection." (p. 3) That one sentence is supported by multiple lines of evidence: fossils; embryology; molecular genetics; geographic distribution of species; atavisms and vestigial organs. There is no modern understanding of biology without evolution.
My point isn't so much that the naysayers against evolution are wrong (as a matter of fact, however, they are). My point is that Darwin's theory (elevated by modern science to the scientific definition of a theory - a fact) obviates the need for a designer. Since the mechanism for most of evolutionary change is natural selection, then the mechanism is not special creation. The mechanism need not be divine wrangling from some cosmic distance to jiggle life into the right dimensions. Darwin' s point was that, given enough time, natural selection was a powerful enough force to result in all of the diversity on display in the natural world without artificial intrusion. No designer was necessary. For life.
There are atheists who are so for no particular reason; perhaps they just don't like church, or they prefer to live life according to their own way; and this is fine. The odds that a personal god exists are so infinitely small that the prospect is virtually impossible; whether or not you can explain why isn't necessary for that to be true. But, the more conversant you are with the theory of evolution, the more prepared you are for the "God of the gaps" arguments that are employed against us. They (and by "they" I don't just mean those trying to convert you to a religion - these days "they" include those looking for your vote!) say that since science doesn't have the answer to a whole host of questions, then God must have - indeed, must be - the answer. Understanding evolution gives you the power to know that science has answered some really hard questions(!) and the wisdom to know that on the answers science doesn't have yet, to paraphrase Dr. Richard Dawkins, we're working on it. And, just because science doesn't have the answer, what on earth makes you think religion has it - religion's track record is pretty horrible, after all.
Evolution is not religious dogma. The fact of Darwinian evolution is scientific knowledge that can give all of us, particularly atheists, important perspective.