Yes, this is a new thing AFAICT. Magazines that frequently published reader content didn't have to sift through quite as vile content when going through letters - death threats and the like have always been a thing but somehow we've lost the cost of creating vile content in this modern era. I've never heard of anyone getting a visit from the FBI over vague death threats on facebook.
This kind of content came with the internet, not social networks. Traditional forum moderators have had to deal with really vile content for a long time now, along with the operators of almost any other media sharing website.
Unless you want to make it illegal for individuals to widely share content without going through an editor, this kind of problem isn't going away any time soon.
It really depends on how any particular site functions. Some sites function better than others. For example, "this kind of problem" doesn't seem to plague us here on HN.