This was one of the main principles our nation was founded on, and for good reason. Jefferson, Adams, and the other Founding Fathers were aware that the typical history of great empires, kingdoms, nations, and civilizations of the past was to start off with a small, benevolent government, but it would always become corrupt, power hungry, bloated, intrusive, oppressive, top-heavy, bureaucratic, and eventually collapse under its own weight or rot from within. Their goal was to word our Constitution and set up our government in such a way that the STATES had almost all the power and the Federal government was little more than a clearing house, a facilitator, and would represent an association of the states in things like foreign trade, diplomacy, or a combined military. The individual states were to have complete control over all things not specifically given by the Constitution to the Federal government. This was designed to accomplish two things: minimize the power accumulated by a centralized and inherently power hungry government, and to make the individual states somewhat competitive with each other for talent, wealth, populations, etc. In other words, if you don't like how one state does things, you can move to one that you like better.
Unfortunately, and directly against the clearly stated reasons of our Founding Fathers, the Federal government has steadily eroded the rights of individual states and assumed more and more control over marriage, education, morality, health care, and just about every other aspect of life. Education, gay marriage, abortion, and just about all those other matters should be left to the individual states to decide, not the Feds.