I still think mainstream news have a larger role in this, social media are followers. People share news stories as if they are true, with context often omitted, manipulated or outright fabricated. But people still trust their news.

CNN, NYT, Washington Post, HuffPost, Vox, Fox News turned into extremely biased sources of disinformation and blatant propaganda.

E.g. a fabricated story in The Atlantic magazine, citing anonymous sources, was repeated and amplified by all these major media hubs and then further by social media for weeks. It's like a giant wave after wave of misinformation and rumors presented as facts. The burden of evidence apparently no longer applies.

The bias is mostly on the left wing of political spectrum, but the right wing are not too far behind.