Tom Gilson tells us, “Three things explain it, in my experience with them”:

1. It’s All About Science. All About Science.
They’re not just The Party of Reason, really. They’re the Party of Science-and-Reason. The hyphens signify the way atheists treat them as joined at the hip. Just this week I heard from one who said he wanted “evidence,” not “philosophy.” But “philosophy” in that case was just thinking through some facts. Why wouldn’t it count for him? Probably because it wasn’t science.
Science has a special lock on reason in this crowd. It’s not because scientists’ reasoning processes are better than logicians’ or historians’ or even theologians, though. It’s because science is “objective,” “self-correcting,” and therefore “less biased” than other lines of thought. Now, this is partly true: Science has successfully corrected many errors, from geocentrism to phlogiston to “physics is complete, there’s nothing left to discover” in the late 19th century.
Defensive reasoning is contained reasoning. If it can’t find truth inside its boundaries, then it simply gives up trying.
To think that it’s objective and unbiased, however, is to crown science with jewels it cannot wear. Science is a human project, not a mechanical one. Scientists can lock themselves in biases as much as anyone else. And even at its best, science comes up with wrong answers. Like geocentrism, phlogiston, and “physics is complete.” …
Tom Gilson, “Why Do Atheists Think They’re the Party of Reason When They Reason So Poorly?” at The Stream (January 15, 2022)
See also: At Salon: New Atheists Accused Of Intellectual Grift And Abject Surrender Now, it’s being attacked among the In and the Cool in Salon, mainly for espousing free speech.