Subsidiarity in the context of the US Constitution is called Federalism
In a republic that protects the freedom of its citizens, what needs doing is done at the appropriate level, which is often the state or county or municipality and NOT the federal level. To keep all the different levels of human grouping intact and respected (family, work, city, county, etc) democracy must resist centralizing and becoming totalitarian. Why should federal authorities demand unisex bathrooms in a city in Arizona that doesn't want them and can't afford them? It is no business of the feds. YOu will say "This is a moral duty" but that is the point "Who says so?"
