> There's no real solution to this problem.
I disagree, There IS a solution, but no one likes it.
Segway: Football aka Soccer had a problem back in the day. Games became (more?) boring because teams would go up a goal, and just play "kick the ball to the goalie". Goalie'd pick up the ball, bounce it, pass to a player who kicked it back to the goalie, rinse and repeat. Then they instituted the back pass rule - https://en.wikipedia.org/wiki/Back-pass_rule - where basically, pass back to the keeper and he can't use his hands, only his feet. A generation of goalies had to learn to play with the ball at their feet, and the bit people enjoyed happened more often.
Rugby Union has had a similar evolution, although more intense. Rugby's goal is to have a game that can be played by people of all shapes and sizes, and they mostly succeed. George Gregan was a great player at 5'9", and most second rowers are over 200cm/6'7". But rugby always gets boring, because the coaches start to playing boring rugby (lot of kicks, lots of positional play, less running). So rugby, every few years, overhauls the rules. For a year or two, the game is exciting again, IMHO the best sport in the world, then it is boring all over again as coaches play safe. We then get another overhaul.
I think the Soccer back-pass rule and rugby's ever-changing-rules are models of how changes in rules can dramatically affect the quality of an activity, I don't think they are doable for online sites at scale. Instead, the only solution I can see working is to constantly change to new platforms.
I started in SEO in circa 2001, and there were heaps of forums run on phpBB et al. They had all recently started, so they were figuring themselves out. The forums all interacted, but they all had their own feel and their own rules. Over a few years, they developed "personalities", and everyone could find a place that suited them. This "personality" then morphed into a kind of group think, and the forums grew into echo chambers where the rules where strictly enforced to keep out the others, and each forum became hostile to all the evil others, and they devolved from fun places to hang out to the same old same old.
SM then came along, with sites like FB, Digg and reddit being born, and this process started again. A new place, no real rules yet, and it was the same exciting process of discovery. Over time, the bad parts set in, and these places became stale echo chambers filled with all the bad bits everyone talks about.
That's why I think the only real solution is to tear it all down and start afresh, because this process has repeated several times now. I think that partly explains why SnapChat and the other platforms exist, and why, IMHO, SnapChat et al will grow to a point then fail to grow anymore, as the "freshness" fades, and all the nastiness intrudes. Unless sites can figure out a way to change this process, which after almost 2 decades of this process is either unlikely (pessimistic), or it is too soon to tell (optimistic).
TL;DR when a platform gets entrenched, it starts to exhibit more nasty traits, and a new platform started afresh is the only solution.