That's what fundamental (really) means: getting back to basics, originality.
So the RCC and EOC are fundamentalist? Yes, perhaps that can be agreed. And maybe there's more fundies than meet the eye.
It is not so long ago that internet atheists and skeptics generally took the firm view that the RC Crusades, the Inquisitions, the forced baptisms, the censorship, the abuses of RC schools, convents and other institutions, the association with Nazism and fascism, gave more than enough reason to be atheist or at least skeptical. But Christians persuaded them that there was no correlation between those infamies and the precepts and practices of Jesus and his apostles; and that
they represented those precepts and practice, as the contemporary, peaceful, harmless and genuine presence.
But now atheists and skeptics have performed an amazing
volte face, and have turned a total blind eye to the offences that once kept Christians up half the night, night after night. And those Christians actually persuaded the knockers that there was indeed correlation between actions and theology, and that literalist, fundamentalist beliefs did indeed give rise to violent actions. They persuaded them that the Reformation really had occurred, that every single Reformer regarded the RCC as antichrist, and that only the Protestant Bible of 66 books was to be used as the final arbiter of Christ's faith, the one and only way to return to the original religion, without the appalling corruptions that had entered Europe, usually by
diktat and coercion, in the long Dark Age. The argument took a long time, but there was eventual success.
Now, twenty years on, it seems that success has been taken too far, much too far. Now, RCism and Eastern Orthodoxy, far from being the villains of the piece, are the real deal, the original! Now, internet atheists and skeptics, who used to mock 'fundies' for their literalism, buy into the literalism of 'This is my Body'. They really believe in Transubstantiation. It is truly a miracle, how an atheist can believe in a miracle.