Are there any states in which the tide is flowing the other way? By that I mean towards complete secularization of public education?
The other option, that of teaching comparative religion, always struck me as impractical. Which religions do you teach? How do you represent those religions? How do you 'compare' them? What strikes me as an eminently reasonable approach is the "Theory of Knowledge" module in the International Baccalaureate. Teach the students to think for themselves and question knowledge itself.
It is a very delicately balanced issue on a knifes razor edge. On one extreme religion is taught, on the other it is disregarded. Both are very dangerous. To disregard it is to basically block off any attempt to understand it, confusing and limiting, hindering a persons own path to knowledge, and forcing it to be taught creates a dangerous boredom where people tune it out. Its all a personal thing. Philosophy of Religion teaches the merits and demerits of each religion, starting with the primitive ancient ancestor worship, all the way to the big 3. The funny thing about this is that it took someone questioning the catholic faith to prove that God isn't gonna strike you down for wanting to know more and learning to question, or Martin Luther would have been burnt to a crisp on the churches steps as a heretic.
My faith, as a christian says that you can share it, but not to force others to follow your path, as it is yours and yours alone.
There was a secular teaching movement in the 90's with an alternative school I dont know if I am spelling it correctly but Montessori? They tried to teach a religion free curriculum based on "Knowledge" The best way to teach religion is to first define it, Religion> Reglios> To tie or to Bind. Faith and religion are two different things. PH said it best, "Religion is a man made construct. But faith is entirely personal." Like the biggest common denominator among the world's religions is a shared understanding of the basic values of the culture where it is born. Also almost every religion in the world has gone through a reformation or two. Like Buddhism is a reformation of Hinduism, etc.
Your point and questions are valid, but its missing a big question: Who would be qualified to teach it? Since religion is just a gathering of people who share the similar faiths, how would we choose someone to objectively teach it, since it is a deeply personal thing? I also tend to believe that many religions almost require you to question things, not just to satisfy personal curiosities, but to also open up doors to learning more and more about what you believe in, or even the polar opposite, to see what is really going on.
Someone once told me that you should be an atheist in school. I called bullshit on it, because some of the biggest scientific discoveries in human history were discovered by people of faith. For example "The Grandfather of the study of Modern Genetics." was a bored, curious monk with a Pea garden. Did his religion or faith have anything to do with it? probably. I mean after his chores and prayers were done, he spent time in the garden, writing down his discoveries. Some argue it could have been anyone else, but I say no, because most people were busy surviving, and only he had the time to fuck around with pea plants. I have never encountered a religion that said to not think for ones self and not to question anything. I have encountered people who use religion evilly, to control and enslave, but strip the bullshit, and the faith is there to guide, not control. Thats why I separate Faith from Religion. But maybe one day all faiths can be taught without people feeling its forced down their throats. Remember religion started with a question: Who made the sky mad?