On nihilistic relativism I don't know why these denialist completely disregard the very likely possibility that the material (for lack of a better term) world is real.
Just apply Occam's Razor; line up your theories and pick the best one. If you have any common sense at all, then it will be the very likely reality, that reality is reality.
Furthermore, reality is really nothing but the reality in which we find ourselves in, whether that is, could be a dream, illusion or whatever, it is entirely moot, as empirical evidence is still the best lead we have. There is nothing else around and it is the only trail of breadcrumbs you have. So the rational thing to do is to examine it and see where it leads. The only other choice here is killing yourself and anyone reading this is clearly not ready yet to test out that option. So it simply does not matter if there is some magical illusion spinning demon as examining those illusions is still our best option.
However, the idea that there is a demon spinning illusions is unverifiable, which means it is about as realistic as the notion that there are mini unicorns that crap gold and gems living in the swears of New York. So how is investing so much of your belief system in an unverifiable entity any different than theism? It is not, and in essence it is the same thing.
These denialist don't even believe their own nonsense, they still eat don't they? They still sleep, shit and type on their keyboards. They claim one thing, but yet they behave as if everything was real, as they realize on some level that is the more likely case and the safest bet. And when you say one thing, yet do another we call that hypocrisy