Why are the 10th Amendment and Necessary and Proper Clause in conflict?

Answer 1

They aren't necessarily in conflict. Very few Acts of Congress are passed via the Necessary and Proper Clause, so most Federal Laws don't infringe States' rights. When there is a question of whether Congress has overreached its authority, the law can be challenged in court. The federal law may or may not be upheld, depending on the courts' interpretation of the Constitution, which changes over time.

Generally, use of the Necessary and Proper Clause (aka Elastic Clause) of Article I, Section 8, overrules the Tenth Amendment (aka State sovereignty, statutes, ordinances, etc.) on the basis of the Article VI, Section 2, Supremacy Clause, provided the particular law enacted under the Necessary and Proper Clause serves a legitimate government interest and is upheld as constitutional.

This doesn't contradict the Tenth Amendment, but does limit its application. The federal courts don't automatically support federal legislation, however; there have been many instances that the courts have found in favor of the States.

Article VI, Section 2 (Supremacy Clause):

"This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding."

Tenth Amendment:

"The powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people."