School uniforms are not a weapon to suppress the poor. They are implemented to protect them.
The reason they are implemented in low-income schools is to prevent the singling out of poor students and reduce bullying. In areas with extreme poverty, the students who cannot afford nice clothes, or rely on hand-me-downs, could be targeted by bullies. The introduction of school uniforms benefits schools in low-income areas more by making children safer and reducing bullying.
They are also a good way of improving classroom behaviour by removing distractions and reinforcing the teacher/student hierarchy. In lower economic areas, classroom discipline is often a recurring issue. Adopting a mandatory school uniform policy is helping to improve student behaviour in these schools.
There is not a malignant campaign to subvert and suppress the lower echelons of society. School uniforms are simply being deployed in an effort to make our schools safer and improve classroom behaviour, which would have better learning outcomes for all.