The laws of Texas as well as the other 49 states are not made in a vacuum. They are not made with total disregard for the Union; indeed, they cannot be, for even before the 14th Amendment there was the "full faith and credit" clause of the Constitution.
State laws, and state constitutions, have evolved within the environment defined and defended by the United States Constitution. To take any one state's laws and constitution out of that environment would require considerable and rapid evolution of that state's laws from a state within a federal system of government to a sovereign nation, beholden to none but its own people.
States' rights advocates--at least this states' rights advocate--do not seek to abolish the Constitution, merely to restore the original order of the Constitution, delineated most clearly in the 10th Amendment, reserving powers and rights not defined to the people and to the states, not to the federal government.