I agree with you. I do find your choice of word "decency" troubling to me. Dress codes are often about control and shame of the poor and in a prison visitors lobby that seems about right. This seems less about decency and more about telling poor people their clothes are not nice enough for a prison which is kind of funny considering prisons are purpose built to be among the worst places in existence in our society.

Trashy is sort of a slur on the poor. Not trying to call you out or anything, maybe there's a better word that trashy aka saying a person is like trash.