The “so what” is related to the fact that people aren’t telling others they have a permit from the pope, where the implied consequence is that the gullible person loses some money. They’re telling people that, for example, immigrants are the cause of all their problems, and that climate change isn’t real. The result of that isn’t that the gullible people are inconvenienced. The result is that they vote, en masse, for people who are actively hurting nor only them, but also the non-gullible people who are part of the same city/society/country/world. They do this based on information that is often provably false, but that the gullible people still believe, especially when it comes from someone in a position of power.

And that valuable service you mention, where gullible people become less gullible, never materializes if all the gullible people ever see is their own echo chamber, which continues to be disconnected from reality. The person with the pope permit to mine black holes has convinced enough people that he's definitely legit, and now he's digging a mine beneath your neighborhood, which will one day cause it to collapse, because there's gold in there and he can get rich selling it on the side. If you're willing to live with that in order to maybe, eventually, teach the people who bought into his permit a lesson, well, that's your call.