People absolutely are mocked for changing their minds. Public debate is a on spectrum from (rare) good faith discussion with good intentions to (more common) playground posturing where changing your mind is seen as a form of weakness.

And weakness must always be punished.

I have no idea where PG puts himself on that spectrum. But SV culture is notorious for being convinced of its own awesomeness. So it's possible that if someone is being mocked it's not because of a change of mind, but for other reasons.