"
One common feature of radicalism is a confidence in the rightness of your ideas, even if they go against those of society at large."
He sounds pretty confident about that.

"
So why do radicals have so much certainty?"
Easy...they mistakenly believe their ideas represent the society at large.
You know, like this guy writing the article and the lab coats in it who are pretending their social science theatre is actual science deserving the credibility of actual science are doing.
All it's really about is BSing people into believing they represent the thoughts of society at large. They don't.
Fucking radicals.