It’s a common mistake to think that folks like the parent commenter are trying to engage in an intellectually honest discussion.

I'm under no illusions they're commenting in good faith, but at times I find it valuable to highlight that fact.

It is valuable! Thank you for doing it.

"Hark" goes the sealion, "sources?"

Well that is kind of the point though, I asked for sources because it is clear that the comment, containing a false and baseless claim (as evidenced by the inability to provide one single supporting source), was not intellectually honest. If we don't challenge these things, then others will start believing them.