So I think that when you notice that feeling, you should stand up for the sanctity of your mind. Even listening to that stuff puts gunk in your gears. You should have called the guy out (politely) for depriving people of the ability to help each other reach a better understanding of things.

I expect that he would have responded that if people are afraid their contributions will be criticized, they'll be less likely to share them, depriving the group of their potentially valuable contributions and risking creating a hostile environment. And he'd have a point, since fear of criticism is normal, and anything which makes people less comfortable with putting themselves forward is likely to filter people out.

If you're not discriminating with respects to beliefs or viewpoints, then you'll see yourself as standing to lose much more by discouraging sharing than discouraging criticism. If you're too undiscriminating, you risk believing stupid things, while if you're too discriminating, you risk filtering out potentially valuable input (which is why we rarely tell newcomers here straight out to "read the sequences" these days; asking that much is too strong a filter.)

In order to convince him that he ought to be allowing criticism of ideas in the discussion, you'd probably have to convince him that he's not intellectually discriminating enough. It's not a simple, one sided proposition, it carries a lot of inferential distance.