Here is a simple example. Atheists argue that the world is not as we would expect if God had created it. Therefore the world must have evolved and God is superfluous. Notice that this makes evolution a fact, not merely a theory. Sound familiar?
And notice that this is a religious argument. It depends on assumptions about what God would and would not create. It doesn't matter whether the science supports evolution (it doesn't), one way or another evolution must be true. Here is an example from PZ Myers, writing in the LA Times about how he analyzes religion:
We go right to the central issue of whether there is a god or not. We're pretty certain that if there were an all-powerful being pulling the strings and shaping history for the benefit of human beings, the universe would look rather different than it does.
That is a religious argument. Myers' conclusion depends on what he believes about God. God wouldn't make life difficult. God wouldn't create patterns in the fossil species. God wouldn't create similarities between species. It makes no difference that evolution does not explain how life, in all its incredible forms, actually arose. It does not matter that evolution is consistently wrong--it must be right. Our religion depends on it.
Evolutionists such as Myers have been duped by religion. They use it and they depend on it, but they imagine they are free of it.