Two very different kind of systems can produce very similar results. "people choosing more or less private clubs" is an apt description of many fringe religions / cults which eject people who question the narrative and tell their adherents to cut off friends and family who aren't in the group. The Jehovah's Witnesses come to mind in particular, they're very different from Facebook but they nonetheless polarize and radicalize people.

Private clubs are not necessarily bad, but ideally they should moderate for basic decorum. If they moderate for ideological alignment, they frequently become radicalization machines; echo chambers where people get their biases reinforced without being challenged.