PBA: I think you’re not right about this. Many “MO” Shuls have full members who are M’chalel Shabbos. They are accepted as people, though their Chillul Shabbos is never condoned (just not publicly condemned). I once Davened in a very left-wing Shul and a Balabas gave a D’var Torah at Shalosh Seudos about how considerate a Rabbi must be because he can’t give Shiurim on things his Balabatim aren’t Makpid on. The Rabbi then publicly responded that just because there are people who have trouble with some things the Torah says doesn’t mean we change what the Torah says. He said what everyone does on a personal level is up to them. But it’s his job to educate and guide, not to pander.
I do hear your question about RIETS. I’d actually be very curious to hear if they would have a reasoning behind that.