Wearing uniforms is mandatory for school children in majority countries. Although children are forced to buy new school uniform, i believe that wearing uniforms can avoid bullying between children. This is the reason why the benefit can outweigh the drawback.
Schools are not only for a middle or high income family, but also for a low income family. As we have known, every year or may by every six months, we should buy a new school uniform because the previous one become ugly and it is expensive. For example, in my country, we need to spend about $20 to buy a new school uniform and it is not a small amount of money for majority of us in Indonesia. However, I believe that school children still need to wear a uniforms.
On the other hand, wearing school uniforms can avoid bullying between children. If school give a freedom to their children and children have a right to choose what they want to wear, a children from a poor family can be bullied by other kids that come from a rich family. The reason is, a children from a poor family can only afford a cheap t-shirt while the other one can afford a high branded t-shirt, etc.
In conclusion, having our school children to wear uniform is better than give a freedom to them to wear everything they want even though children are forced to buy a new one.