Over the decades, I've seen a great deal of evidence to support the hypothesis that, no matter what faith they might nominally adhere to, Fundamentalists of any creed have more in common with each other than they do with more moderate adherents of their own creed.
From my observations, the common keystone in the Fundamentalist worldview is this:
We and we alone know the One True and Proper Path, and those who disagree with us are not merely in error, they are evil, they are our enemies, and any abuse we can deliver unto them is not only justified, but for their own good.
All too often, this becomes the Fundamentalist's primary tenet -- the specific details of his or her faith all become a distant second to the pure, blind assertion that I am right and you are not.
This is their true religion.
Proportionally, I've seen just as many Fundamentalists who think they're Atheists as I have Fundamentalists who think they're Anything Else, and their reaction to Thoughtcrime is just as zealous.
Did that last sentence piss you off?
Might want to run some diagnostics.