As you have probably heard a million times, you cannot legislate morality.
I agree that the slaveowners had set up a legal system they used to squash the moral human rights of blacks that continued well up into the 1960s.
By 'slaveowners' you mean both north and South. Right?
While there is no question that the slave and Jim Crow societies had power and legal standing, they were not just powers because they were based on institutionalized violation of human rights.
Which is another good reason to keep this debate going. A man should not have the legal right to enslave another man. A government should not have the legal right to deny those 'self evident truths'.
There's no doubt that slavery was the albatross around the neck of state's rights. By wars end, the slaves had gained a measure of freedom but all the citizens of the newly reunited states had lost a great deal of freedom.
Nobody really believes that, not even the people who say it. And they are referring to sexual morality only.
What the heck else do you think we legislate? Why do we have laws against anything? Because we believe they're wrong, or IOW immoral.
By 'slaveowners' you mean both north and South. Right?
By 1861 there were no slaves in "the north." The most commonly accepted boundary between the sections ran precisely along the slave/free line, for exactly that reason.
Some southern/border states stayed in the Union, but that didn't exactly make them northern states. It is also relevant that all of these "northern" slave states freed their slaves by state action before the federal government freed them by constitutional amendment, with the exception of KY and DE.
What enormous expansion of federal power was there in 1880 as compared to 1860? Not much. Most of the expanded federal powers went away again after the war. Most of those that were retained for a while during Reconstruction was because some southern terrorists refused to accept blacks as fellow citizens. The terrorists eventually won that one, for most of a century.
There is no question that (white male) Americans have less freedom from government rule today than in 1860. But I contend little of this is a direct result of the WBTS. A great deal more of it is as a result of the renewed expansion of federal power that started in the late 19th century in the not well-named Progressive Movement, then really picked up steam under Wilson and Roosevelt. But while the War certainly set some precedents for federal power, there is no direct line of descent between the federal powers of 1865 and of today.