This is a phenomenon known as group polarization or attitude polarization. This occurs in person as well. It's just what happens when people of similar opinions get together --especially groups that don't know each other very well. There are numerous theories explained in detail on Wikipedia though.

Perhaps it's more common online since the internet allows people to connect with just about anyone worldwide. People are able to find communities for even the most niche of topics, and online communities have a tendency to become echo chambers.

Personally I have a tendency towards black/white hyperbole when leaving comments on Lemmy for instance because if I make it too grey the meaning will be misconstrued. Inevitably. Every single time. (see, I just did it again)

I also have a tendency towards adding jokes to negative comments, even to serious subject matter, as I’ve noticed both online and in real life people are more likely to dismiss outright negativity if you don’t make it funny somehow. People are scarcely in the mood for serious discussion of real problems, especially of those they can’t solve

Knee jerk reactions are easy, all you need is emotion and a single impetus. Nuance is more complicated and can be difficult to fully express. Most people don't try to make things more complicated than they need to be and don't put thought into everything they say or post.

When we talk to each other face to face, the words we choose are only one of an enormous toolkit of resources we have to communicate the nuances of our messages. When I call someone a piece of shit, you can tell how I really feel by everything else that goes with it. How loud am I being? Am I smiling? Am I shrugging? Am I talking fast or slow? Nonverbal cues (e.g., gesture, facial expression, eye gaze, posture) and paralinguistic cues (e.g., sighs, laughter, pitch, speed, volume, breathiness) make it really easy for the same exact words to communicate a million different things. If I say “he’s a piece of shit,” you can infer from all this other stuff whether I’m really upset, whether I’m expressing empathy but not investment, whether I’m being entirely sarcastic, whether I’m just having fun swearing…whatever. AND if you’re not sure what I mean, all it takes is a slightly confused expression from you and I can immediately clarify.

When you take the conversation online, we lose all that. When I write “he’s a piece of shit,” in my head it still comes with the million flavors of nuance it could have in conversation. When you read it, you get none of them. Everything comes off literal and straightforward. This is the problem that things like emoji and \s are attempting to solve, but nothing will ever really replace all the context of conversation.

I’m not saying it’s good or bad. Maybe we need to learn to use a wider range of “linguistic colors” to be more effective communicators online. And maybe there’s an element of cultural reproduction too: nobody starts out meaning to sound a extreme s they do but then the internet just starts to feel like an extreme place so we expect that that’s how we should talk in this context. I’m not sure about how we SHOULD talk online, but I do believe the cause of what you’re describing isn’t malicious, lazy, or otherwise ill-intended. I think it’s just things lost in translation.

Hyperbole and other superlatives are very common forms of lying, because “everyone” knows that it isn’t literally true, so if you call it out you look like a pedant, but it still has a greater emotional impact than an honest representation of the situation, so it’s a lie that gives the desired outcome of painting your picture without the risk of reputational damage if you are caught in the lie

Why do people tend towards the most extreme expressions when describing things?

It's because extremes tend to present the expected picture better than vague "it's kind of like this and a bit of that..."

I think it's a combination of lack of vocabulary, projecting a story online to their own similar thing and responding to that, and just people using a lot of hyperbole which can sometimes be misunderstood in text.

But yes, I agree, people on the internet are the fucking worst.

Piece of shit is mild in my book, thats basic level of asshole. From there it goes up to shit-head, pile of shit, fucking goddamned heap of shit, and further. But piece of shit is just a starter asshole.

Hyperbole: https://www.dictionary.com/browse/hyperbole

Because every one of them is dumb as fuck

Because ballbags don't deserve nuance, mostly. My nuance is saved for things that don't tick me up a couple degrees on the internal thermostat.