You could say the same about child abuse. That doesn’t make it not disgusting or unimportant. If you have to hide the things you are doing to children from the parents, you’re doing a bad thing.
The notion that it’s a school’s place to usurp the parent’s choices of how to raise the kid is the problem here. If the majority of the parents oppose that, the school shouldn’t do it. It’s a public school, it should serve the interests and desires of the public.