Every state gets to make its own decisions. UNLESS, of course it’s a territory that wants to become a state where slavery is legal. Then that schit right there is VERBOTEN. Why? Because we say so in our new and improved interpretation of the Constitution.
Does that mean a state gets to legalize incest? How about pederasty? Sutee? Cannibalism? How about plunging scissors into the back of the skull of an infant as she is traveling down the birth canal? On your logic the answer must be "yes". But the Declaration teaches us that only "just laws" can be derived from the consent of the governed. Consent as such cannot justify anything intrinsically immoral. Your statement above is a crystal clear expression of the legal and moral positivism that undergirds everything you wish for just as it undergirds the entirety of the radical Democrat party of today---the same radical democrat party that once claimed human beings are actually chairs and dogs and oxen, just as they now claim a man is a woman and vise versa.
