"We also see examples of subcultures or even cults, but again by modern standards they are incredibly tame, and are never potentially destabilizing to culture."

Eh, the "Eaters" cult on the island in "Consider Phlebas" which is definatly a culture citizen cult seems to be quiet extreme- and the AIs do not interfere, even as the obliterate themselves. The AI in look to the windward commits suicide, because it can not escape the memory that makes it who it is- which contains the obliteration of its twin and the humans remaining on orbitals.