The issue is that when a church rents out their building for a wedding ceremony to non-members, it becomes like every other commercial enterprise, and should be subject to the same non-discrimination regulations as every other commercial enterprise.

If churches want to keep everything merely to their own members (and there are lots who have that policy), that's fine. They have every right to absolutely control every jot and tittle of their membership. They have every right (in the USA) to discriminate as part of their membership.

It is only when they open up to the public that they have to obey outside laws against discrimination. If they only hire workers from within their membership, they can force them to follow their own rules. But if they advertise to the public for workers, then they can't.

It's the difference between private workings and public commercial offerings. It is a silly red herring to suggest Baptists going to a Methodist church and demanding changes. We are discussing a church offering commercial services to the public, and then wanting to discriminate against portions of the public.

AA isn't offering commercial services to the public. Public buses were offering commercial services to the public. Notice the difference.