Because that individual doesn’t have the power to enforce their personal freedom. The Principal does have the power to enforce their idea of what the “correct” look is. The principal isn’t concerned about raising conditions for the group in actuality, they just want reality to conform to their idea of what they desire it to be. For them, it’s within their rights to their own freedom to bring everything that makes them uncomfortable to heel. Anything that they don’t like is an affront to their personal freedom to make everyone do what they want.