I'm fine with that... but these platforms aren't.
These platforms are driven by what Eric Weinstein, correctly I think, calls E.G.O.s, or Embedded Growth Obligations. You can't convince a venture capitalist to fund something like Twitter without the promise of enormous user growth, because the model only works if you have an enormous userbase on the platform.
I actually think Zuckerberg's dumbass tag line, "It's free, and always will be." is stupid. Facebook is worth about jack shit to everyone except advertisers, because it doesn't cost anything. Putting up a monthly fee is how you separate people who are willing to shit all over something from people who are willing to build something.
World of Warcraft is, I think, a fine example of this, especially versus a game like League of Legends. WoW's userbase, will still filled with the occasional troll and troublemaker, has far fewer than League. Why? Because you have to buy the game itself just to get started. Then you have to spend $15 a month to play it. You're invested from the word "go". For League, you play the entire game, from start to "finish" for free, only paying if you want to. Hence you see a ton more trolling and shitty behavior, because the vast, vast majority of players aren't invested - its just a way for them to while away their lives with no investment.
I guarantee you, if you had to pay $5 a month for Twitter and $5 a month for Facebook, you'd see a lot more reasonable behavior, because after the first few months, only people who really got "value" from the platform would keep spending the money to use it. And the sad part is, even 100,000,000 users at $5 a month would be an enormous moneymaking enterprise - with almost guaranteed higher quality interactions.