It's not really new, even going back there were flame wars and shit-posting on BBSes before the internet was common. It tends to come with relative anonymity.
It takes curated communities in order to overcome. Some places do better than others. It's also all to easy for biases to become policy in some of these communities/sites which can wind up almost worse than the shit posting to begin with.
20 yrs ago, most of the Internet users were teenagers and very young adults.
Most of these people are in their late 30s to 40s now. Did new kids join too? Sure! But if you look at the birth rates of our societies, you'll notice that it's a bell curve. Consequently, the average age is going up.
Furthermore, there is a strong selection bias with this demographic: the happier they're, the less likely they're going to be on these platforms, because they'll prioritize family, hobbies or whatever else over ... Well... "shit posting with random strangers".
Ultimately you're left with a significant chunk of people that are often disgruntled, jaded or outright mentally unwell.