I detest the idea of uniform and all the petty rules that go with it. I'd find a simple uniform item acceptable (something like a school jumper with logo) to identify pupils as belonging within the school, but the way it's enforced now is nonsensical and owes a lot more to the older generations' constructions of childhood/youth than anything else.
Part of growing up and preparing for the workplace is learning how to dress for different situations and following dress codes. I've never heard of any child attending a non-UK, non-uniform school who grew up and couldn't cope with the sartorial requirements of their chosen career because they hadn't been made to wear a uniform for 14 years in preparation. I agree with the point on the other thread that if it was about work preparedness then business suits and a certain amount of make-up on girls would be the expectation, not ill-fitting blazers!
Uniform is often overpriced and poorly-fitting (because young people's bodies aren't all the same shape! Imagine requiring all the women on this thread to wear the same skirt from the same shop in whatever standard size we're closest to. Some it would suit very well, and some would look awful. Most teenage girls are even more self-conscious about their bodies and looks than adult women.) The enforcement of some of the rules seems to owe more to John Locke's ideas about preparing a child for life through physical discomforts than anything else - blazers at the height of summer, no coats or boots allowed in winter, etc. The 'social leveler' argument strikes me as misleading - it's very clear who is wearing old or second-hand uniform, and children are generally aware of each other's socio-economic status and not in a state of ignorance about it. It's also part of life that some people are richer than others. If children are being bullied for this, it's the bullying that needs to be tackled, not the way pupils dress. Otherwise the bullies will just pick on something else about their victims.
A common argument is that children stress so much over what to wear on non-uniform days that it'd be a nightmare if every day was like that - but it's only that way because it's a novelty. In non-uniform schools in other countries (and in universities here), most young people dress casually. And someone dressing like a goth or having pink hair or whatever is only novel the first few times you see it. After that, it's just how Jane looks. Unimportant. Schools claim that they don't want young people to focus on their appearance and not their studies - this could be dealt with very simply through rules that you can't re-apply make-up or fuss with clothing during class. Instead, they make appearance more important to young people as they have little control over how they present themselves for much of the day. This is actually a common tactic in institutions, to want people to 'look the same' and discourage individualism. I disagree with this for philosophical reasons.
Lots of teachers don't want to enforce uniform rules and resent having to spend their time doing so. There are a few who are over-zealous about it to the point where it becomes a power game between them and students and that's good for nobody involved (my younger sister was sent home, missing a day's classes, for wearing the wrong colour hairband, FFS). Schools should be about learning, not about conformity, and I've yet to see a good argument that uniforms improve learning.