That cult wasn't in the Culture. It was on an independent orbital (Vavatch) that the Culture was attempting to evacuate before destroying it to prevent it from being conquered by the Idirans.

I read Vavatch as anarcho-capitalist in contrast to the Culture's anarchism.

Vavatch had a lot of stuff going on that wouldn't have been allowed in the Culture. Certainly the Culture wouldn't have allowed them to non-consensually eat other people. The other stuff probably wouldn't have been prevented by force, but they would vigorously try to convince you not to do it and to prevent you from convincing other people.