In a recent question, the questioner, the answerer and a commenter all used variants of a new coinage: "alternative fact-ing", "altfacting", "alt-facting".
That posed a challenge.
If they had said the person was "wrong" or was saying things that were "wrong", I would leave it untouched. The evidence should demonstrate that.
If they said the person was "presenting the other side of the argument", I would leave it untouched.
If they had said the person was "lying", I would take action to change it. Calling someone a liar implies not only what they are saying is incorrect, but that they know it, and they are deliberately misleading people. That is not something we can demonstrate with evidence - it is about motives.
I consider it defamatory, but more importantly, I consider it beyond what the evidence demonstrates.
So, where in the spectrum does this new expression lie?