People from outside the UK might think after reading these posts that we in the UK have some national brainwashing scheme to turn people into obedient zealots for the State Religion, and that we urgently need a constitution, a division of church and state, and a whole slew of new laws either making this sort of thing illegal or compulsory, depending on their faith or lack of it. This is the UK folks: and some of us actually prefer to wing it rather than to set everything into laws and let expensive lawyers deal with it.
Anyhow, RE classes in the UK aren’t really ‘incredibly important’ - they way I think science or maths is. They are one period a week where, if you aren’t goofing off or staring out of the window, you may get exposed to the fact that some other people have some other beliefs. The title suggests that they do not need to address atheism at all, but the curriculum is so woolly that it is not unreasonable to bring it up one week. This exposure to religion is sufficiently slight that it probably serves as a vaccination against the full-blown disease.
I do not know why the particular teacher put that bit in the letter, but I feel they must have been provoked to make such a stand for something as harmless as the RE school expedition. A mass boycott by one faction would probably do it. Anyway, all’s well that ends well, and everyone at that school now knows a bit more about religious diversity.