conspiracy theory hijacker

Conspirators or patsies who join conspiracy theorists with an intent to discredit them in the eyes of the general public.

CT: Presidential election is staged by the Illuminati.
Victim: Surely this cannot be true, let me prove it to you.
CTH: It's true and the Earth is flat and run by lizards.
Victim: Now I won't even bother.
CT: Don't mind him, he's with them, he's a conspiracy theory hijacker.