This isn't new either; the legacy version was the systematic denial that smoking caused cancer. This has been going on since the 1950s, and is still being litigated. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3490543/
The result of this is that any single point of fact-determination becomes a target. It's good of Facebook to take some kind of stand against the most fraudulent and racist articles that get circulated on there; the "blood libel" against Jews and so on. But now they're dragged into the other conflicts. There will be a lot of money available from Exxon-Mobil to deny climate change, for example.
Ultimately the concept of "fact" as something outside subjectivity will be destroyed. The rotation of the earth around the sun is really just your opinion, right? /s If heliocentricity were politically convenient or profitable there would be an astroturf campaign promoting it on facebook.
(A subgenre of this is libel lawsuits, which are much less of a problem in the US due to "anti-SLAPP" laws: https://www.medialaw.org/topics-page/anti-slapp?tmpl=compone... but may be a significant problem in the UK; e.g. https://www.theguardian.com/media/2009/dec/17/bbc-trafigura and https://en.wikipedia.org/wiki/McLibel_case , lasting over a decade)