There is nothing that prohibits secession. Thus, it would be legal.
If secession is illegal, then a) revolution is the only alternative to redress wrongs and b)states are indeed subservient to the federal government, contrary to the Constitution.
According to the supremacy clause of the Constitution (Article VI, Clause 2), U.S. Constitution, Federal Statutes, and U.S. Treaties are "the supreme law of the land" within their sphere of powers, so a state can't simply declare that those laws don't apply to it or within its borders.
Secession would be possible if Congress agrees and enacts a law to that effect (or possibly through a constitutional amendment), but not unilateral secession by one state or group of states without the approval of Congress.