People haven't changed. There have always been trolls, malcontents, crazies. Attend any public hearing, ask any fan club or newspaper mail room.
As a new medium, the distinction of the web is significantly lowered transaction costs. No different from email spammers.
Yes, but now the seductive idea that one can improve the world by getting one's teenage hormonal aggression out on somebody "who deserves it" is beamed into people's living rooms and onto devices in their pocket, complete with calls to action. How many teenagers do you know who realize how morally bankrupt this is, vs the number of teenagers who are actively enthusiastic about some idea like this?
And, how many people do you know who are past their teens who still haven't "gotten it" yet?
Also, it's an unwarranted assumption that teenage aggression is only held onto by teenagers.
You're probably just emotionally invested in memes and feel hurt when I point out they implicitly espouse shallow and prejudicial positions.
Or in other words, there's a world of harm that can be done by putting a huge number of these malcontents in contact with each other in a way that they can all cooperate, with laser focus on a single subject.
The Internet not only has increased the range of hateful groupthink, it has made a large number of people believe that it is somehow noble and elevated. It almost seems like there's an anti-intelligentsia of forum manipulators who see the creation of new and pointless forms of prejudice as a kind of sport.
I have the growing impression that there's a growing segment of people online who see their outrage and any acts motivated by it as the expression of some kind of enlightened vigilante justice. It just so happens that the worst crimes against humanity were motivated by people who thought just like that. Unfortunately, it's the single best way to blind yourself against your own evil deeds while making it likely you'll get trapped into irrevocable courses of action.