The internet has given a voice to every idiot on the planet, but they were idiots nonetheless. Yes, the curtain of anonymity lets you get away with anything, but honestly, does it really affect you what ShagYourNana69 from GodKnowsWhere really thinks or says of you? These are non-stories the media digs up, because it gets the people riled up. Promoting idiots at it's finest.
But you have to take into account who are using also these social media sites. Children wont understand so easily what is said wrong in those threads. It also comes down to education and environment/parents. But the influence twitter for example gives is huge i think. Add some youtube/twitch videos where people play games and might be more directed to racism. Twitch is working on this and gives hard ban to these people but this content is still available to people who are easily manipulated.
About catching people who say these things. That is easy even if they would try to hide their *** with some free/cheap VPN, but will they do it? Nope. Noone wants to use so much resources on catching so many twitter hate messages, but it would give out huge signal.