This discussion reminded me of the powerful saying:
"The Laws of United States protects the Believer. Not the Belief."
That said, I know many people of a number of faiths. Most are not believers but find comfort in the familiar culture they were born in to. I doubt very much that atheists are to blame for radical fundementalism of any stripe. Much more, I will say that fundamentalism breeds more fundamentalism and "culture war" rhetoric.
Personally, and politically, I do my personal best to avoid becoming ideological. I am certainly biased, but evidence must have the final say, which makes what we accept as true dynamic and fungible.
How can that attitude be to blame for the rise of radical fundamentalism of any stripe? That people prefer faith over evidence may turn out to be biological. If this is the case, you can hardly blame non-theism, but instead blame the primitive organ of thought. The Brain.