I think something one might learn over time from different sites styled like reddit and lemmy is that they are not monoliths,

There is a comment above that says the same thing, but in practice, think about it like, any give post attracts both people that agree, and disagree with it, generally strongly. The vast majority don't engage with it.

Because of this the opinions seem both stronger, and more common. But realize that any given comment thread is a microscopic percent of even the highly active users, and always a biased sample.

With regards to echo chambers, this is why I personally oppose blocklists or how on reddit you can make something 'private'. Pretending something that is problematic doesn't exist does nothing to deal with the problem. I see this as fundamentally how r/TheDonald came to be, and reedit was fundamental in building the modern white nationalist movement. Through blocking and going private, r/TheDonald shielded itself from outside criticism, so that users didn't see alternative view points, and specifically, were protected from open mockery. Originally the sub started as a troll/ joke but quickly became the defacto headquarters of the largest funnel for white nationalism the internet has ever seen. It might seem a bit over the top, but I argue that Trumps 2016 success would not have happened with out specifically r/TheDonald. Its why all of the 'truth social' and extended media took on a reddit style interactivity. It was the birthplace of the MAGA movement online. They morphed it into a self referential echo chamber, and used purity testing to filter out potential critics. Eventually it was banned entirely, but not until long after the damage was done.

So I don't agree that ideas should be shielded from criticism. The problem with that is without criticisms, they can take hold, and grow legs of their own. But at the same time, you shouldn't make too much of things when you see a strong binary online, because almost any internet discussion will be inherently polar (because only those who agree disagree with a principal or idea will be drawn to discuss it; 95% of everyone else just doesnt care).