Google and Facebook are private advertising companies at heart. So yes, they get to decide what (in theory) is best for their business on this issue. If they believe curbing what they view is "fake news" is best for business, they have every right to do so.
Someone can set up a social network entirely funded by the "fake news" Google and Facebook rejects, if they believe that this is a valid business model too. Again, they have every right.
It only leans "fascism" or "North Korea" style if news editorial direction becomes dictated by the government, and dissent is stifled by force.