[nonameiguess]

This sounds perfectly ethical to me but it's not clear what value it provides. People who are part of the same church or gym already have the opportunity to get to know each other by being in the same physical community in the first place and don't need a website where they can interact with the same people but online. If they do want that, they're likely to just set up a Facebook group. While the obvious disadvantage there is now Facebook owns their data, but it's also free and most people are going to choose free.

Ironically, online venue for a real-world network limited to verified members of that network was what Facebook itself originally was, until they realized opening up to everyone was the difference between a novelty for college students and a multi-trillion dollar world eater.