I do think a big part of it is this format, social media forums, & internet in general. it's become big part of our interactions and without a face to face it's really easy to just generalize the dissenting opinions of one-liner typing names and meme-reposting faces and fit them into a very convenient package which you have a pre-loaded response to. it dehumanizes the interaction and you wind up not arguing with another person, but fitting them into a category of enemy to which you assign all the negative attributes and prejudice you want to associate with someone who'd disagree with you.
in some ways it's kinda like road rage. people get ripshit pissed at other cars violating their idea of how things should go, and a big piece of it is the removal of it, the lack of recognition that these other people are actually people and not just obstacle boxes impeding your box.