I mostly agree with the author in that everyone shouldn't be on one platform and that yes, Twitter, Facebook, etc., aren't anywhere close to ideal sites for actually forming strong relationships and having good discussions. I also agree that the separation of internet self and real self has all but vanished from the internet, despite my own personal attempts to retain it. Additionally, as someone who has spent their formative, adolescent, and even current years being parts of independent communities on the internet, I can assure you that there were people out there who knew what was being lost and what the problems were as Reddit, Facebook, and the others became the hubs for everything.
However, the author makes references to things like MUDs, IRC chats, web forums, and then antagonists like "random internet Nazis" (come on dude) and Gamergate of all things, and I can't help but feel that the author of the article is part of a intellectual group that appeared after things like internet forums, transient chatrooms, and video game servers. It's very popular to try to "dunk" on sowing doubt in a case like this because everyone cites that "Yet you participate in it. Curious!" comic in some way or another, but I think the doubt is warranted in this case.
The author may have been around when those things were active, but expressed no deep interest at worst or a passing interest at best in any of them until centralization became a problem to think about, and SUDDENLY all of those things captured their attention. A HN poster who doesn't really care about non-techie niche communities but puts on big airs about caring because rebelling against centralized monoliths like Twitter is part of (hacker) counterculture/social signaling.
The author didn't have to deal with being a powerless normal user as internet Nazi groups infiltrating communities they were a part of, never had to watch independent sites and projects get absorbed into Reddit and its abhorrent community; it's all just a fun intellectual thought puzzle to ruminate on with a buddy at a bar and philosophical soapbox to stand on with their web blog and Twitter account. The author even boils it down to political pundits retreating to private circles, which completely separates it from the real experiences of loss of and yearning for smaller communities.
We've read this same song and dance here on HN almost weekly if not daily here on HN: everyone's glued to their smartphones, Twitter and Facebook control all online content, return to tradition, yadda yadda. I don't really know how this comment is going to be taken but because of all these things, I find it very difficult to believe the author isn't subject to the tyranny of likes and internet attention himself, and that the post reads more as disingenuous intellectual fellatio than anything else, intended to resonate with those who closely follow hacker culture on HN for traction.