Doubtless you can post examples of "rabid secularists" saying this? It certainly isn't for example what either Dawkins or Dennett say. I am as rabid a secularist as anyone, and I wouldn't dream of saying that the clear fact of evolution proves that God doesn't exist.
Or did you just make this up or read it somewhere. I've asked for people to back up this claim up and every time all I've got is chirping crickets in response.
In fact, Dawkins is one of those I had in mind. It was Dawkins who wrote that "Darwin made it possible to be an intellectually fulfilled atheist." He also said, "The more you understand the significance of evolution, the more you are pushed away from the agnostic position and towards atheism" (www.simonyi.ox.ac.uk).
Stop and contemplate those statements for a moment. Science is an approach to understanding the natural world that explicitly eschews supernatural explanations.Therefore, natural science cannot be used to "prove" the existence of God; likewise, it cannot be used to "prove" the nonexistence of God. By itself, science cannot push one towards atheism. Science is simply the wrong tool for the job—much like using a telescope as a screw driver.
But Dawkins goes much further. He has publicly attacked religion as being opposed to science and reason. For a sample of his statements, you might check the Positive Atheism web site.
Now, when Dawkins says that evolutionary theory pushes one toward atheism, I realize that he is talking religion or philosophy, not natural science. Unfortunately, the scientific community does not rise up and say so. Scientists have circled the wagons against the Creationists, whom they accuse (with good reason) of misusing science in the service of religion. Yet the same scientists are strangely silent when one of their number misuses science in the service of atheism.