Dred Scott simply read Article IV of the Constitution into a fugitive case. The Northern States weren't playing fair with respect to Article IV: they wrote unconstitutional ordinances, and then abolitionists organized rings to help runaways. Not exactly calculated to help intersectional relations, ya know.
And the South's interest in acquiring territories to the west that the planters could move to was always lively since before the annexation of Texas. Okay, the Northwest Ordinance prohibited slavery in the Old Northwest, fine. But just as the anti-slavery faction politicked for that Ordinance's passage, so pro-slavery people in the South politicked to get Stephen Douglas's Kansas-Nebraska Act passed into law in 1854. Are you saying they shouldn't have been allowed to do that?
Especially since northern states didn't have the same slave-holding traditions that the south had when the Union was formed.
Slavery was just as legal in the North as it was in the South in the colonial period and under the Articles of Confederation. Some of the early slave-revolt conspiracies were hatched in New York City in the 18th century.
So those who claim that the South seceded due to states rights are in the untenable position of having to defend the Souths' violations of those same states rights, when they tried to get slavery legalized in the north.
So not true! Article IV was in the Constitution from the git, and the language of its Section 2 was crystal-clear. Repeat, the South didn't try to "get slavery legalized" in the North. Their legislators legislated on the subject of slave versus free in the Territories, and the compromise was Popular Sovereignty, which the South signed off on -- but the North had a problem with! (So much for having a vote!) What did happen was that two individual slaveholders who were deprived of their property by state ordinances in contravention of their property rights confirmed by Article IV, went to court. One was the Dred Scott case, prior to which SCOTUS had ruled in Prigg vs. Commonwealth of Pennsylvania in 1842 that a Pennsylvania law forbidding seizure of fugitive slaves was unconstitutional. The Northern States had responded to Prigg by passing a raft of fresh anti-slavery statutes, basically asserting State sovereignty under the Tenth Amendment against Article IV.
The third case was the Lemon case in New York, referred to by David Donald in Lincoln (1999), which appeared to Lincoln and the other freesoil Whigs, Republicans and Free Soilers like a companion piece to Dred Scott, but I don't think it was ever taken up for review by SCOTUS.
This is the real issue. Until the South pushed it in the 1850s, the issue, though very real, was a dying issue as far at the North was concerned.
No, I'm sorry, that isn't true. John Quincy Adams and the Abolitionists fought like hell all through the 1830's and most of the 1840's to keep Texas out of the Union (first request 1836), and as I mentioned, many of the Northern anti-slavery statutes in the North dated to the 1840's.
So a Northern apologist bears the burden, which I've never seen your side taxed fairly with yet in these threads, of explaining why slavery was the issue, and not anti-slavery, over which the Civil War was fought. Given Lincoln's actions with respect to the South, clearly the latter is the case.