There is no way to 'bind' safely
I agree.
and you think children should be at liberty to send anything they like to other children without a teacher or an adult taking a cursory glance over the content?
Did I say that? No.
You said the school was promoting this. Which is patently untrue. The school is not promoting it, a pupil-produced newsletter included some links.
You are trying to whip up outrage by making it seem like breast binding is an officially promoted practice to all pupils coming from teachers (the school). Which it clearly is not.
I'm as gender critical as they come, but for god's sake have some standards and the pride not to engage in this Daily Mail-esque "won't somebody think of the children??!" crap. Use your brain and consider the actual information at hand, not just what you want to see because it shores up your position.
Let's deal with facts and not extrapolated idiocy.