This isn’t an argument against school uniforms, it is an argument against making parents pay for them.
Surveys indicate that when parents are asked whether or not they would support school uniforms if the school had to provide them for free, they typically support uniforms. This indicates that it is not the mandatory uniform policies that are a problem, but the financing of the policy. 
There is nothing wrong with mandatory school uniform policies. However, to avoid placing an additional financial burden on families, they should be subsidised or paid for by the school rather than the parents.