The I found the main points of the article interesting and fairly convincing but you seem to over-correct for correspondence bias when you say
"If the allegations about Wikipedia are true, they're explained by ordinary human nature, not by extraordinary human nature". Even if normal human behaviour leads to cultishness, why assume that individual psychological quirks didn't have a relevant effect in a specific case?
"One word for probability one is "certainty" and a word for probability zero is "impossible"."
I think you should be cautious about using these words like this, at least if you might be talking about uncountable probability spaces. Using your definitions it is certain that (say) a normally distributed variable takes a value in the real numbers but impossible for it to take any such value.
I hope this isn't unfairly pedantic to point out. I can see that one could argue that for decision making in the real world you only assign probabilities to finitely many outcomes.