You know what the "Interfaith"-concept reminds me of? Conspiracy-theorists.

[Act_of_Reparation]

8. Two caveats:

The First:

The guy with the bottle of homeopathy pills might not say it outright, but he still believes the guy with the alien microchip in his brain is a fucking nutcase. Sure they're respectful, but it's a superficial respect in which everyone agrees not to tell anyone else how they really feel.

It works fine for brief, banal interactions, but it's not viable in long-term relationships. Once the homeopath discovers microchip man supports increased FDA regulations on useless sugar pills, the saccharine friendliness will disappear.

The Second:

The homeopath and microchip man both hold fringe beliefs. They can get along relatively well because there's the tacit understanding that neither of them commands a single shred of influence beyond the confines of their tiny subculture. They get along because they're stronger together and there's no tangible benefit to be gained from attacking each other.

The situation is reversed for numerically superior belief systems. They have little to loose from attacking other religions, and actually risk losing followers if they appear to lend alternative belief systems even a shred of credibility.

That's why interfaith movements tend to be small, quiet, and have virtually no impact whatsoever.