Once again, apart from safety in specific lessons, what does a child's hairstyle have to do with school and why are parents allowing schools to dictate how their child looks when they only spend 20% of their time in school?
It has no impact on learning and you could equally argue the same for uniform, however at least with uniform, they can remove it after school and wear their own clothes. They have to have a school acceptable haircut all the time.
They are actually worse than the military and at least people in the military have a bit more flexibility and have actually chosen to be there.
And before people start saying that you can choose a different school, many people don't actually have a choice and also many schools have the same draconian rules.
my DC attended one of the top state schools and whilst it had a uniform that was generally adhered to, no-one was sent home for wearing leggings instead of trousers or skirt or for shoes with bits of colour on them etc and their hair/facial hair was their own business. I've seen boys with long loose afro type hair, boys with full beard, DC with coloured hair of various styles. As long as there is nothing to cause offense, they are able to have what they like.
Funnily enough they achieve highly in terms of academic success and the school has very little in the way of discipline issues, bullying or LLD.