Now we are seeing a large group of people freely sharing misinformation amongst themselves. The fueling of this, I would argue, is outside of facebook and is being brought there by the people themselves.
It was really easy to blame the lowering of the level of discourse to social media. However, the "our side at any cost" has its modern seeds in the advent of right wing radio with Rush Limbaugh, followed by the rise of fox news. With the internet, the public has learned that they too can be players in the political landscape by commenting on news articles. All of which predates the rise of social media to a large extent. In the early 2000s, Yahoo News political articles would have 10s of thousands of comments, even now, the 2020 election market on predictit had 300k comments on it, of people posting memes and s*t talking to each other.
This is the culture now. To change this, you can't go and regulate a social media company, you have to change the culture.
All of this was evident many years ago, based on the ad delivery system Facebook built, and the kinds of information their early APIs were exposing to people. It didn’t take a genius to realize having people building more and more sophisticated systems to spy on people to get data to drive the development of products to persuade people was a dangerous flywheel, and one that was held up by good intentions (making services “free”), so it was likely to be sustainable via an “ends justify the means” rationalization.