The issue really isn’t about media leaning left or right. Truth is like science, on a fundamental level it isn’t up for debate. Journalists like policemen, only really serve society when they follow a code of ethics. For a journalist, it’s partly about intending to pursue an objective truth.
Now Facebook may be a conduit for and profiteer from Fake News, but they don’t actually produce it. We as a society need to hold them to account in the same way we hold any business to account whose business model depends on advertising. Public preassure can work to do this, regulations can work to do this, litigation can work. (Imagine if the ad of Denzel endorsing Trump had been on TV? Lawsuit, of course. Why not do the same thing to Facebook?)
A bigger issue is probably the producers of fake news. The three decades of daily, non-stop, anti-science ignorance that is Fox News. Oddly, the biggest fish isn’t even mentioned in this article. Because it’s successful and popular and so, normalized and mainstreamed to point it actually moderated a debate as if it hired real, ethical journalists. If a society can normalize anti-science propaganda like Fox News, how can anyone be surprised that it would also elect a lying racist bigot like Trump?