Exactly. Anything can be a religion. Which means that absolute religious liberty is the same as anarchy.
Not so much necessary as inevitable, maybe. Like music, mental pattern-building is built into people - and the logical levels do not reach a top level. There is no highest logical level of pattern. So humans reach the highest level they can handle, bootstrap and meditate until they can't get any farther, and confront the spiritual realm, by nature. And when they do, they by necessity establish culturally conventional or standard modes of handling it. Compare music - a universal aspect of human existence in its abstract possibilities, but each culture establishes some particular way of actually being musical, of making and employing the actual sounds. No one makes music in an abstract or universal sense - they build particular instruments, sing in certain ways, and partly by circumstance - making do with what's at hand. Nomadic pastoralists make music without pianos and orchestras. And so we get religion(s). Nomadic pastoralists pray and worship without priests and cathedrals - that affects their range of beliefs, relationship with ritual, etc.
