Why is it important that government schools do not promote any one religion?

A school is a premise where the children, who are the future of a nation goes to study, so inculcating good attributes in them is necessary for nation building.

Children who go to schools are of different religions, so giving priority or promoting any one religion would make other students feel inferior.

The government schools are run by the Government itself, so if the government would not abide by the principles of the Constitution then how the normal citizen would follow them. Hence it is necessary that this institution must be free from communalism.