I'm not going to pretend that social media companies don't have a role in all of this because they absolutely do, but...
I also think that they provide a platform and ultimately it is the people who produce the messages and the people who consume them that are at fault here.
The fact that there is a means of communication that I can use to distribute lies and idiocy and provoke violent reactions doesn't mean that I have to or that I should.
Similarly the fact that there is somebody out there using that platform to send out messages that are clearly unbalanced or inflammatory or hate filled doesn't mean that I have to listen to them, absorb them and react in an equally ridiculous way myself.
Yes, the increase in access to information and various news and opinion sources does mean that people are going to be exposed to a lot more crap, but it equally means that they have a lot more access to fact check and get other balanced opinions on things.
We should not expect the messengers to censor and control all communication that passes through social media platforms and the criticism that they would receive if they did would be just as great as that they receive for not doing so.