Remember the Star Trek episode, where after generations of rote repeating, "We The People" had turned into "E Pleb Neesta"?
I remember when the teacher told us we weren't allowed to beat up on the Jehovah's Witness kid who was NOT ALLOWED to say the pledge, because yeah, in his church it IS "idol worship." Of course, when did that ever stop kids from ganging up on the outsider weird kid?
Me, I think the answer is very simple: Privatize all schools. No tax money for schools, period. There's no question of tax money going to religious instruction then.