Atheiststm with a super-capital A, the ones who scrounge around subreddits like this in a perpetual fever of sorting by /new seeking debates, are by far the most insufferable; self assured, pedantic, dull, eye roll inducing, headstrong, dorks one could ever fear to encounter.
I think it’s primarily the total lack of serious doubt. The type of doubt they profess to extend to others, but seemingly never orient toward themselves. The idea of “what if I’m wrong?” scarcely truly enters their mind at any point. They’ve bought into a mundane worldview where all is reducible to “just atoms” or “just chemicals”, with no authentically justifiable philosophical awareness for inferring that. They’ve just inherited the modern worldview of what essentially boils down to a tacit endorsement of “scientism”, and run with it, seemingly making it their sole life goal to “debunk” whatever higher thoughts people have about the world.