That's because this conversation is occurring in the abstract - surely you can think of examples which don't fall into your supposed pattern (flat earth, pizza parlors, etc.)
But those are super edge cases, the vast super majority of things aren't clear cut at all. "Is that policy going to increase employment? Will it depress wages, and by how much?"
Good luck with judging who's right and who's wrong.
These "super edge cases" are happening monthly. THAT's the problem. The examples given weren't a historical review, they're a sampling of what happened in 2019! If these were in any way rare or outside the norm, I'd feel safe ignoring them, but even in cases of absolute truth and fact (jade in your vagina does not cure anything) we get a netflix series.
Yes, in a world with literally billions of people, you have a few millions who believe outlandish things. If that was the extent of the problem with polarization/toxicity on the internet (or public debate in general), I doubt we'd talk about it, and I'd be very happy with the state of the world.
Those people have no large base, no stable membership, no money, no power. Focusing on them is like decrying the fall of science because 6yo Timmy still believes in Santa Clause.
You say "millions of people believe foolish things", and then completely disregard exactly how many there are and how concentrated they become. I disagree with the assertions at the end that "a few million" do not constitute a large following, and allow me to provide a few counterexamples:
* the Flat Earth Society has a very stable membership and patreon. Mark Sagent's youtube channel alone has 58k subscribers. Social media influence is the source of money, and a power all on its own.
* Gweneth Paltrow's pseudoscience has a facebook group with 500k members. She has a netflix series and a reliable income from her online storefront. The facebook group came first, then the netflix series.
* QAnon is a persistent conspiracy theory with no basis in fact. Regardless, tripcodes (a public hash of the password used for identity verification on 4chan) denote a persistent online identity, so he's got a following... and the following is what causes power.
Power in its purest form is asking someone for something and getting it. This looks different in the modern age than it did previously, but saying that celebrities don't have power belies the entire concept. These are celebrities, either advocating obviously false things, or due to their advocation of obviously false things, and millions of people are taken in.
In contrast, the expected Iowa caucus turnout numbers are going to be around 60,000. Or, in other words: There are more people believing in flat earth than there are democrats caucasing in Iowa. How in the world is this not a problem.
> Or, in other words: There are more people believing in flat earth than there are democrats caucasing in Iowa. How in the world is this not a problem.
I mean, isn't the answer already in these sentences? The world vs Iowa.
It's not that I don't believe pseudoscience and cults are a problem, it's just that they are a small problem on the grand scheme of things. Increasing polarization of society at large is a problem on a different scale. It's something that has very tangible effects for most people, some guy believing that the earth is flat and having 60k people watch his videos really doesn't.
9-11 was a super edge case. Yes, absolutely it's difficult to make firm judgements about many issues, but we should still pay attention to edge cases because even though the people out at the edges of discourse seem nuts doesn't mean they're not serious or motivated or capable.
Sure, sure, but "serious, motivated and capable" still doesn't give them leverage. You will always have individuals committing terrible things, there will always be the next school shooter or terrorist, but those are, while tragic, small events, and if you didn't turn on the TV, you usually wouldn't notice them if you lived a few hundred miles away. Change the policies of a nation and you'll have a much larger effect that can be felt everywhere within its borders.
So sure, paying attention to the edge cases is fine, but focus most of your attention on the big issues.
Changing policies is the point of terrorism. You seem to be assuming it's randomized and atomized rather than itself being networked and (loosely) coordinated.
That's not rationalism, that's just saying "I'm right, they are wrong, end of discussion".