There are deeply committed Catholics and deeply committed Protestants, as well as relatively nominal or culturally affiliated members of both.I think your statement that they "reject the theology" cannot be sustained, but it could be true that tradition plays a bigger role in Catholoicism, but protestantism itself certainly has its own traditions.

Taking one's religion seriously does not by itself constitute fanaticism. Flying a plane into a highrise because you think that is what your religion commands certainly is. That is not to say there aren't any Christian fundamentalists out there, there certainly are. But just because you do not relate to a religion, or religions in general, does not automatically make everyone who disagrees a fanatic.