Ideology follows many of the same basic structures as a religious belief system, in many cases ideology is a subset of a religious belief system, but in this case it's not. Combine that with the extreme polarization and demonization of the other side*, one of the oldest propaganda techniques ever[0], you end up with cult-like mentality. Even some circles (on both sides) will have love-bombing [1], a technique used to recruit new members. I grew up in a cult (Jehovah's Witnesses) and went against my dad when I was 16 to get out of it. Once you've been though that stuff and come out on the other side, you can't help but not see it in the modern political climate and it's disgusting.
Are they in a cult? That sounds like some Scientology shit.