Well, there's no shortage of so-called "Christians" who believe all kinds of stuff that isn't in the Bible, right? Pro-gay marriage, pro-abortion, all the rest. How did those people get convinced?
Educational system, communicate of doubts, raise opposing views, debate, etc.
Therefore, instead of sending troops to Islamic countries, we should send a multitude of our liberal lawyers, judges, professors, journalists, actors and politicians to sway them, or at least, establish laws to thwart them.
'Liberalism is a mental disorder' - Michael Savage