I've unfortunately lost a few friends to this process (why I felt compelled to comment). There's definitely a "rabbit hole" effect where there's a chain of beliefs that lead you further into extremism. A, B, and C may be "extreme" but benign, and then at some juncture, D comes along and that's the 'thing' that confirms their extremism is a correct response to the world.
I had this happen with an online friend who forgot he was talking to a mixed-race black man and started sending me what was effectively racist content (under religious pretenses), completely doe-eyed, almost leaning in as to see whether I was just as excited to "get on board" (I wasn't). That shift happened rather quickly and I later stitched together how he'd gotten there in his head (in effect online religious content on YT/Twitter).
That's the danger with entertaining extremism: one day, they won't be "just talking about stuff," they'll be strapping up the proverbial vest and you'll be thinking "but we just had a normal conversation..."
I care when they start arguing with me and trying to jam their belief down my throat. I didn’t even ask, you brought it up and you’re mad at me because I disagree.
I think this is the more interesting point to consider. Having a belief, any belief, is probably just fine. It’s the second part that’s the issue.
As to your question, there are a lot of extreme beliefs that sometimes end up becoming true. IIRC the person who first advocated for washing hands because of tiny "things" that could make people sick, he was laughed out of the room, and he was right. It was an extreme belief at the time.
I basically reject the whole premise that "no belief is extreme" because there are countless examples throughout history of extreme beliefs that the world considered extreme, and they turned out to be true. Didn't make the belief any less extreme at the time.
One of the most depressing things about exploring the conspiracy world is that all roads tend to get co-opted into hateful rhetoric - I miss the days when I believed that one could hold a rather silly belief and have it just be benign.
Once you accept a premise that majority consensus of well informed people can be drastically wrong, it's not hard to then transfer that horizontally from one domain to another. So if you accept the possibility that scientists made up climate change - why wouldn't they also make up COVID? or falsify risks associated with vaccines? or any other number of things.
Underpinning all of this is some basic elements of humility and empathy - willingness to accede to a greater authority of others, and to weigh others experience that is different to yours as important in informing your views. Cutting those tethers gives your own belief system a new degree of freedom.