Yes! Thank you for reminding me.
People have rights while government, state or federal, have powers.
Exactly, and those powers should be constrained as much as possible.
Thinking through the ‘how’ behind the establishment of a State religion, especially in historical contexts, flies in the face of individual rights. Having a State religion, in the past, meant that citizens of said State (nation state, empire, whatever) don’t have the right of conscious in choosing their own religion but must express fealty to the religion of the State.
Everybody can clap all they want if it is a religion they like, but as soon as you open that door, you now have given the State powers to establish an official religion that opposes your views. (and you can’t say ‘just move’ either because as soon as you give the States powers to tell you want to believe, you are giving them enough power they can tell you where to go, what you can or can’t say, where you work, etc so state-to-state mobility could be out of the question.)