“You seem to forget that the SCOTUS ruled that slavery was legal in the Dred Scott decision.”
Not exactly. They ruled that since there were no laws banning slavery in the south Dred Scott had to be returned to his owner. The question before the Supreme Court was not whether slavery was legal, but whether someone had the right to confiscate someone’s property by moving it across state lines. While one can argue on both sides of the case, one also has to recognize that SCOTUS was actually doing what SCOTUS should do, ruling on constitutional law, and not making moral decisions having nothing to do with the constitution.
Dred Scott still holds the record as the worst decision in SCOTUS history, despite recent strong competition.
Its biggest failure was that they went well beyond ruling on the law, as most of the language of the decision was not needed to rule on the case itself.
The Court announced that Congress had no right to restrict slavery in territories, despite the fact that it had done so going back to before the Constitution itself. Taney also, historically and legally inaccurately, stated that people of African ancestry, not just slaves, were not and never could be citizens. This is despite the well-known fact that blacks had fought in the Revolution and had the right to vote in several states at the time, including North Carolina, a southern slave state.
Taney just wrote in whatever he wanted in his decision. There is good evidence he coordinated his decision with southern politicians in Congress, at the very least a violation of judicial ethics, and some that he was working on a decision that would have invalidated northern state laws outlawing slavery in their states, waiting only for an appropriate case to attach it to. After all, if the Constitution prohibited the federal government from keeping a man from taking his property into a territory, how could a State keep him from bringing his property with him when he moved north?