Gab is for the fringiest of the right wing. And people often cluster disparate ideas together if they're all considered to be markers of membership within their "tribe".

Leftists, or at least those on the left wing of liberalism, tend to do this as well, particularly on social and cultural issues.

I think part of it is also a matter of not so much what people believe as what they will tolerate. The vaccine skeptic isn't going to tolerate an AI bot that tells him vaccines work, but maybe generally oblivious to the Holocaust and thus really not notice or care if and when an AI bot misleads on it. Meanwhile a Holocaust denier might be indifferent about vaccines, but his Holocaust denialism serves as a key pillar of an overall bigoted worldview that he is unwilling to have challenged by an AI bot.