If you go to a school, you have to abide by their rules. Having limits on hair style is perfectly acceptable in the same way that enforcing a uniform is.
Literally the option in the poll.
Uniform policies and other policy documents are publically available just about on every single school website (at least in the government system). If you don't agree or accept the school's ratified policy, don't enrol your child/ren there. It really is as simple as that.
We live in a world where parents are given freedom of choice (to an extent) as to what school to send their child to. Even in the government school, this is the case. If only every student went to their local school rather than nitpicking...

I don't think most uniform policies are unreasonable, either.
Students need to remember that the reason uniform policies exist primarily relates to the image of the school. Students walk around the local community and are representative of that school. We must also remember that such rules exist in the workplace too.... which I feel that alot of this is preparing students for.
As a teacher I am sadly the devil when it comes to uniform.. if I see a student out of uniform (e.g. wrong shoes) I ask to see a uniform pass from the YLC.. if they don't have one, I ask them to go and get one. So personally I don't issue the consequences which helps my rapport with students but at the same time I make sure it gets resolved.
Or, in fact, for things like piercings, tattoos and the like?
Would you go to an interview for employment with piercings and tattoos clearly visible? I personally don't have a problem with them but the reality is this contributes to a negative image. The society we live in unfortunately.