Man, let me introduce you to Roswell truthers, 911 conspiracy theorist, racists, cryptonazis, biblical biologists/geogrpahists, phrenologists, freudians, climate-change-is fake theorists, anti-vax activists, and flat earthers.

All of them have deniers, and that is the core function. When your core critical thought relies on denial of all evidence or outside data 'my falsehood is as good as your truth' then it isn't critical anymore.

But it looks like critical thinking. Often with an elaborate scientific pantomime built around it.

One of the hardest of modern things is separating the mimes from practicioners. You cannot have sufficient knowledge or reasoning in most domains, the language is tricky, and there are liars, unknowing mimes, and bad actors everywhere. And our brains are actively working against us much of the time.