On April 6, 1846, Dred and Harriet Scott filed petitions in the Missouri circuit court at St. Louis seeking to establish their right to freedom based on their residence on free soil. Under Missouri law they had a strong case. As Fehrenbacher says, "again and again, the highest curt of the state had ruled that a master who took his slave to reside in a state or territory where slavery was prohibited thereby emancipated him." Unfortunately for the Scotts, their lawyer allowed a technical weakness in his case to sabotage the verdict. He didn't provide a witness that could establish that Mrs. Emerson owned the Scotts, even though all concerned knew that to be the case. Because of that defect the verdict went against the Scotts. They filed a motion for a retrial, but the defendant filed something called a bill of exceptions and the case was sent to the supreme court of Missouri. It was not until March 22, 1852 that the state supreme court handed down a decision. The Scotts still had the facts on their side and probably would have prevailed except that the issue of slavery had become so heated in the nation by 1852 that the proslavery justices of Missouri were not disposed to give the anti-slavery side their way. The court ruled against the Scotts.
Which it would have to do to remain compliant with Article IV, section 2.
(So much for states' rights.)
The powers possessed by the states do not include powers that are explicitly removed by the US Constitution. Creating a "free state" is contradictory to Article IV, Section 2. It can't be done, or at least I can't see any way in which it could have been done.
Basically, the court was inviting an opportunity to overturn antislavery statutes in the North.
Yes, because the law was clearly against such statutes. How can you make a statute "freeing slaves" when the US Constitution requires that you return them to their owners? How does that work?