And if my grandmother had wheels she’d be a bicycle. The process of creating an in group naturally creates out groups. The “brainwashing” OP describes is just as natural as social alignment through an innate drive for conformity.
There is a pretty interesting study of a large group of chimps. I dont remember where exactly but they have been civil warring the last 15 years or so. Point is, it seems that there is some kind of innate group formation process.
Conformity I think follows the innate drive to coerce the nonconformant into compliance