It might also be argued that parents who want their children exposed to religious influences can adequately fulfill that wish off school property and outside school time. With all its surface persuasiveness, however, this argument seriously misconceives the basic constitutional justification for permitting the exercises at issue in these cases. For a compulsory state educational system so structures a child's life that, if religious exercises are held to be an impermissible activity in schools, religion is placed at an artificial and state-created disadvantage. Viewed in this light, permission of such exercises for those who want them is necessary if the schools are truly to be neutral in the matter of religion. And a refusal to permit religious exercises thus is seen not as the realization of state neutrality, but rather as the establishment of a religion of secularism, or, at the least, as government support of the beliefs of those who think that religious exercises should be conducted only in private.
-Justice Potter Stewart, Dissent, School District of Abington Township, Pennsylvania v. Schempp
The logical and practical failings of State neutrality have been detailed by many thinkers such as David Schindler. I had not realized that these failings were apparent even in 1963.