[aragonite]

I don't know anything about this particular case, but I believe the term "black propaganda" (https://en.m.wikipedia.org/wiki/Black_propaganda) is often used for the kind of situation you have in mind.

I've often wondered about that with some online interactions. Sometimes, a "defense" of P is so poorly argued that it seems almost intentional, as if designed to provoke the well-sourced, well-argued rebuttals that almost invariably follow immediately.

Logically speaking, these rebuttals should not discredit the proposition P itself, only a particular argument for P (e.g. refuting the ontological proof of the existence of God does not thereby refute theism). But when such exchanges happen frequently enough they can give rise to the widespread impression that P has no smart, thoughful defenders, so the overall effect is similar.