That's fair, but to play devils advocate, every sect can point the finger at some other sect, or at heretics within their own sect. No sect will agree to any negative critique, and because their doctrines tend to be self consistent, critique is pointless anyway. Yet the sects are not completely separate, but are collusive to some degree. And individual beliefs may be a mishmash of ideas from multiple sects. Indeed for this reason, the divisions between sects are not hard edged.

American fundamentalism would have no political power without the tacit consent of the mainstream. The predominant sects in my state are mainline, yet they voted en masse to outlaw gay marriage (before the US supreme court ruled otherwise).