I get this same effect when talking about vanilla non-conspiratorial things, agree with their concerns, and I've been asked what I think. Since I don't tow their party line by focusing my attention on the same bad people, I'm "othered" and written off. This is more pronounced when talking to people on the red team than people on the blue team, but happens with both.
A simple example is "GPS satellites tracking your phone". Trying to explain to people that the GPS satellites only transmit, but that it's applications on your phone spilling your location, so there are steps you can personally take to avoid that - it just doesn't work. It's like my model of the situation doesn't fit into their model, and rather than doing the work to understand what I'm saying, they'd rather continue with their comforting simplistic answer that generally combines defeatism with condemnation.
> I'm not sure what the best strategy for fighting this kind of weird mass idiotic groupthink is
If anyone has any ideas please share them. For basically any social movement, when I see it gets some traction I'll think finally people are starting to care. But then as things progress, the movement takes on a life of its own and heads in the wrong direction without fail. It's like instead of staying focused on the problem, opportunists looking for power supply a "solution" that steers the crowd into an easy non-answer to benefit themselves. And it doesn't take many of them, because once the red herring becomes the groupthink dogma, pointing out its problems gets you othered.
I think the catastrophe we're now experiencing is from the wave of "normies" discovering conspiracy theories. Early Internet denizens went through this phase a long time ago, and had to contextualize wild theories within mainstream thought. Even if we found them very compelling, we couldn't just rant to everyone we met. But now that everyone and their aunt is on faceboot, not only can you repeat all the nonsense you've heard without being socially ostracized, you will actually gain popularity from it!
I think attacking things from the side by targeting how to think critically rather than any specific topic is the best bet. It allows people to learn ideas without being immediately defensive.
Lesswrong is mostly this.
Pretty much everything you said also applies to religion which the vast majority of people in the world believe (in some capacity).
Believing clearly wrong things is a part of humanity - arguably the default - and people have to learn to overcome it.
I used to be someone who would perpetually argue with friends and family members who believed in all this conspiracy crap, usually devolving to me sending links to Snopes and Politifact and whatnot, but I later realized that it was completely irrelevant, and probably just made them feel stronger in their beliefs, since they could always just dismiss me as "in on it" whenever I said something they didn't like.
Nowadays, I honestly just don't talk to family members and (former) friends who believe in really problematic nonsense, since by the time that they've fallen into the QAnon rabbit hole, it's not like a beautiful and logical argument from me to going to have any effect.
I'm not sure what the best strategy for fighting this kind of weird mass idiotic groupthink is. There's a part of me that thinks that the best thing to do is to make fun of them and mock them, but of course that's a lot easier to do when it's not your friend of family-member on the other end.