Oh absolutely. It would have to retain a purely voluntary
status. But of course, theocracies are always possible unless
the laws of the State are strong enough to forbid it.... and
there's no revolution to overturn constitutions. Then again,
even in "milder" theocracies that are primarily democratic in
government, there's enough secular elements for a viable
society. Still, I prefer a freedom-of-religion without state
control but that's mostly because I was raised in a culture
promoting it as a value, so it's hard to be totally objective.