Lots of first-world countries have Internet. Not a lot of first-world countries have the amount of shootings, including mass shootings, the US has. That makes me doubt that the Internet is the problem.
It's not just shootings, though - the bitter rift that brexit has wrought is part of the same problem. Hell, gamergate sits in the category too. All this drives division, which ultimately drives violence.
Brexit is just as much, if not more, the responsibility of the newspapers which have spent so long writing misleading articles about the EU and inflammatory articles about "migrants".
Indeed, but that message has likewise been amplified through social media to the point where brexit became possible. Without SM, I don't think it would have happened.