One of the big downsides of most microblogging platforms (and social media in general) is that they consolidate everything into one undifferentiated aggregation

One of the big downsides of most microblogging platforms (and social media in general) is that they consolidate everything into one undifferentiated aggregation, rather than facilitate the creation of many distinct bounded spaces. Traditional online communities -- BBSes, IRC channels, Usenet groups, even standard blogs -- are all self-contained spaces that have their own norms and expectations, and so preserve the ability to have communities with high standards and high-quality discourse amidst others that fall victim to the kind of regression to the mean you're talking about. HN is a great example of this (as compared to other sites), as is Reddit, where the differences between various subreddits are very apparent. But social media lumps everything together into a single space, where each participant is looking at a slightly different subset of the whole, and this causes the rot to overwhelm everything pretty rapidly.