Well, I couldn’t agree with that part more, since that also happened to me - and to boot, within a parish, and it was all lies – every word of it - and it was engineered by (unbelievably) the lay Director of Faith Formation, who told lies to the pastor (who unfortunately believed her). I surely know about unjustly destroyed reputations.
Perhaps I wasn’t clear in my initial response. I was limiting the hypothetical situation to private message gossip (again, this has zero to do with CAF; I’m thinking of other forums, many of which are way more hotly debated than this one, if that’s possible.

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Assuming two private messagers clearly feel the same way about a poster whose identity they do not know, nor are they in a position to have it revealed, it would seem that the greatest harm would be the practice of destructiveness between the two of them, if it went no further than the two of them. It is still far off the mark from 'building up whatever is right, whatever is holy, whatever is good, whatever is just," etc., but there is no direct affect on the object of gossip in question, as his or her reputation would presumably never be touched since he or she cannot be identified IRL.