What if it were liberal news? This is basically the filter bubble problem. All filters have biases whether they are human or algorithmic.
The problem isn't that FB is slanted, but that FB has a near-monopoly on user attention, which allows its slant to be both covert and disproportionately influential.
If FB was one of a selection of companies competing in the same space, political bias would be less of an issue, because it would be more like the print magazine and blog space.
But then you have the problem that the US gov has an entire network of foundations, think-tanks, blogs, PR companies, astroturfers, bought-and-paid-for journalists, and other "thought leaders" who exist solely to present a specific agenda - usually a pro-corporate one.
In the same way that you can't argue with the Fed, you can't argue with a state-organised propaganda machine - not easily, anyway.
So the problem is much wider than FB.