I ran a BBS from my parents phone line in the early 90s and had as much techno-optimistic exuberance as you'd ever want. Everything you've said here is absolutely true. But I'd narrow it down to two basic laws: 1. The ability to run a site has fallen into the hands of people who have no idea how it works and aren't responsible for their actions (i.e, their personal stake has to do with share value and not maintaining a community), and 2. More importantly, the ability to share content has become too easy for people who aren't capable of any of the thought or curiosity that used to be required to reach a bare level of competence for their private musings to be translated into easily-accessed public speech.

The hurdle of technical competence was a useful, if imperfect, stand-in which barred the vast illiterate masses from creating echo chambers of mutually self-reinforcing ignorance. We all had a right to free speech in the 90s, but no one had a right to be heard. Facebook, Twitter, et al simply lowered the bar to being heard to the point where noise overwhelmed signal.