This would lead to an “eternal September” effect of declining quality.
This has been the way of Internet communities since the Internet started, really. So I don't think anyone (OP included) really believes this whole wild-frontier, brave-new-world kind of deal will last long. But having gone from MySpace to Facebook to Reddit to here, having a new platform at least gives me hope that there will always be a new one to jump to when the current one really turns to crap.
I remember thinking AltaVista was the absolute best search engine for no particular reason, and being willing to die on that hill.
(I did not, in fact, die on that hill)