The point isn’t to argue I think, it’s to inform others that he’s not credible (and he’s free to ‘defend’ himself via argument of course).

But what would make an adult person do this outside of being paid?

MICE - Money, Ideology, Coercion, Ego. Money doesn’t necessarily mean being a paid shill, BTW - Alex Jones from InfoWars makes his money selling supplements, for instance.

I don’t think they’re being coerced or making money from their audience, so Ideology or Ego.