For some people, it’s important to have rules!! Of course you need the standard social construct rules, but the less necessary ones are important too. I think they give structure and consistency to people, so even if they’re arbitrary, it fulfils that need and as long as isn’t disruptive to society, I don’t see the harm. Plus, knowing someone also follows the same rules, rituals and holidays you do gives you instant rapport with them, so it aids in building a sense of community. Polite people outside of the new religion will also be curious and interested in hearing about these rules/rituals and whatever reasoning could uphold them, and the followers likely will enjoy explaining them, so this helps them build friendships outside of the religious group as well.

Tho it’s crucial that others aren’t ostracized for not following the more arbitrary ones and that those that do follow them don’t feel any actionable feelings of superior devotion or what-not. I think you can ostracize people who violate rules that relate to already well established social constructs (theft, murder, etc), but not the more frivolous restrictions and behavioral requirements we’d invent here.