The Establishment Clause . . . stands as an expression of principle on the part of the Founders . . . that religion is too personal, too sacred, too holy, to permit its 'unhallowed perversion' by a civil magistrate.
Approving some religious claims while deeming others unworthy of accommodation could be 'perceived as favoring one religion over another,' the very 'risk the [Constitution's] Establishment Clause was designed to preclude.