States' Rights
Each state in America is unique in its people, climate, history, economy, and geography. This union of unique states is what makes the United States special. Therefore, "one size" does not "fit all" when it comes to governing.
The Tenth Amendment of the U.S. Constitution says that if a power hasn't been granted to the federal government, and it hasn't been forbidden to the states, then that power lies in the control of the states and their respective citizens. Therefore, federal mandates that don't come with federal funding (thereby placing the financial burden on the states) are contrary to the very principle of the Tenth Amendment.
For example, while the legislation was well-meaning, the Clean Air Act, the Clean Water Act, the Homeland Security Act, the Individuals with Disabilities Act, and the No Child Left Behind Act are all "unfunded federal mandates" that states, counties and cities have wound up paying for. The Unfunded Mandates Reform Act, which took effect in 1996, has made virtually no difference - all of the acts listed above were passed after 1996.
The federal government needs to do more than "consider" the cost legislation may pose to states - if the federal government is unwilling or unable to fund a piece of federal legislation, then it shouldn't be passed!
Paul has signed the Tenth Amendment Pledge, put forth by the Tenth Amendment Center.
