My non-religious parents told me I could join any church I wanted to. Then when I announced I was joining the Mormon Church they went apeshit. Inadvertently, they pushed me deeper into it. It's one of the reasons why I don't give my TBM kids a hard time about Mormonism.
I'm starting to get a few deep questions from the older ones.
Rights are artificial and are enforced by the community enumerating said Rights.
Powers are what you can get away with.
Rowdy teenagers lounging on your lawn have the power to loll about on your property. If you have the power to get them to leave, good for you. But if you stand on the front porch and yell at them that they have to right to be on your lawn, they'll just laugh. You or your community, or together, have to enforce Rights. You'll have to call the police and maybe they'll eventually roll a unit to talk to the kids.
It's a balancing act. If after they ignore you, you go in your house and come out with a shotgun, a lot of different scenarios become possible, many of which may involve the Rights rowdy kids have not to be killed for just standing on an old fart's lawn.
But that shotgun certainly does give you Power.
In the instance you cite, 18 year old adults certainly have the Right to quit the church. But again, it's a balancing act. While they have the Right, do they have the Power? If the Army is still hiring, then maybe they do. But if they want to rely on their parents continued support, maybe enforcing their Right will bump up against their parents' Power to kick them the hell out.
You know how many people understand Rights, Powers & Privileges in America? I don't know the exact number, but it could be as few as in the high five figures.