"like all non-Christians they are doing Satan’s work."

At least in my experience, THAT is the core of fundamentalist "christianity" – the notion that your group has found the Truth, and that the Devil is bound and determined to lead you from that Truth. All others are misled *at best* – at worst, they are knowingly doing the Devil's work.

The Devil, meanwhile, mixes 99.9% Truth with that .1% of lie that will lead you onto that downward path.

The harder you try to tell these people that they're wrong, the firmer they are in their belief that they are right. After all, the Devil wouldn't need to lead them away from their belief if they weren't currently on the Path of Righteousness . . . .

So yeah, they firmly beleive that if you are not *just* like them, then you are an agent of the Devil – the only question is whether or not you know it.