Have they though?
I get that stuff like Twitter's character limit inevitably brings down the "quality" of conversation since it's difficult to make a nuanced argument in so few words. But social media has also gotten a lot of people from various walks of life who'd otherwise never meet to interact and empathize with each other.
Have the negative effects of social media been greater than the positive ones? Maybe, but I still think it's unfair to blame the medium for the current state of things.