According to Keith Parsons:
What is also needed is a new and compelling narrative, one that can compete with and defeat the narrative of ISIS and other hateful ideologies…What kind of idealistic message is needed? Well, obviously it must be Islamic. Only Islam can defeat Islamist fanaticism. - See more at: http://www.patheos.com/blogs/secularoutpost/2015/12/16/message-to-moderate-muslims/#sthash.JGmu7OCK.dpuf
So a militant atheist like Parsons thinks only Islam can defeat Islamist fanaticism. That's an ironic concession from an atheist. By his own admission, atheism can't defeat jihadism, Only a better version of Islam can.
And Parsons is half right: it takes a powerful religion to defeat a powerful religion. That's because religion has a fundamental appeal that atheism does not. You can't beat something with nothing.
And that means only Christianity can defeat Islam. A superior religious ideology. Better ideas. And, especially, grace.
Even if some Muslims found atheism persuasive, that only cuts Islam at the root, without planting something better in its place.
Of course, that doesn't negate the need for a military defense.