Toxic.  Unhelpful.  Malicious.  

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We should wonder about the motivations of people who keep posting the same old divisive declarations over and over again.  

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Watch out for extremists or mercenaries (or China or Russia) on Facebook that are just trying to create animosity and discontentment in America.

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ad nauseam:  referring to something that has been done or repeated so often that it has become annoying or tiresome.  ~ Oxford Languages.