This phenomenon cuts both ways. Ralph Nader in the 70s kept telling falsehoods about the health hazards of nuclear power, seemed immune to correction, and had a platform with the press uncritically propagating his claims. (Documented in Petr Beckmann's book at that time.) In retrospect this seems like a hinge point in history leading to our current energy problems.

Someone's incentive towards some point of view is not evidence either way about an object-level claim. It's only useful for questions like attention allocation, or like how someone could be so wrong after you've established they're probably wrong.