The First Amendment to the Constitution says government can't establish a religion, but neither can it limit the exercise of religion. And that's the issue here. What does it mean to be free to exercise your religion? It's not about what you can believe. It's whether you can act on those beliefs.
There are a lot of things that I'm allowing myself to be, but it's a conscious effort to experience contentment for me. My brain doesn't do that naturally. I'm very overwhelmed all of the time.