True as this may be in legal and business terms, facebook is also by its monopoly position a de facto news source and filter and ought to be held accountable for such to public standards of transparency.
Yes, it does not match the nominal definition of a "monopoly", in a sense that those people are free to look for information elsewhere. But they don't, and so whatever narrative FB chooses to feed to them is what they will believe.
I guess you could call it a monopoly on attention.
True, which means laws can be passed to enforce this. Same with tobacco antitrust, trains, water, power, etc. Of course the costs might not be really worth it..