One religious defense is that the constitution guarantees freedom of religion, not freedom from religion. I say that not only is that not true, it's not possible to have freedom of religion without freedom from religion.
Here's a quick thought experiment. You want to go to the BMV and renew your driver's license. However, in order to do that, you first have to say a prayer to Zeus (or some other god you don't believe in). When you're not getting a license you can pray or not pray to whatever god(s) you like, but you can't get a license without saying a prayer to Zeus first. That doesn't sound very free does it?
I don't even know what true freedom of religion without freedom from religion would look like. You can go to whatever church you want as long as you also go to the state-endorsed church? You can follow whatever doctrine you believe in as long as you also follow the doctrine of the state religion?
Freedom of religion means live and let live. You can believe in whatever you believe in and I can believe in whatever I believe in. If we can force our beliefs on the other in any way, it's no longer free.