They had done so since the founding without armed invasion. But I'm not supporting the institution, it was an evil, it's just that your position would grant the federal government the power to invade a sovereign state or states at will, under any pretext or condition, to end any legal practice that it disagrees with.
And if that is true why have a Constitution at all?
Not "any legal practice" and not just when it "disagrees", but rather when states laws are in blatant disregard to the principles of the law or, in this case, the law of God. I would have supported the use of troops to force the end of Jim Crow in the 1950's and to ensure that blacks had the right to vote. The South had made it abundantly clear that slavery and, later, Jim Crow, would end no other way. I would not support troops for just any old reason.