I argue history, not moral platitudes. You sound as though you would have been one of the "laws higher than the Constitution" Republicans of the pre-war period. Would that we were all as perfect as you think you are.
I was once threatened with death for arguing as an adult in the Deep South in the 1950s that blacks should have the same rights as whites. Did you ever stick your neck out like that in such a place or such a time for the rights of others? If not, then I'd suggest you get down off your moral high horse.
I'll try to discuss history with you again to expand your understanding the period. Both fugitive slave laws were ruled to be constitutional by the Supreme Court. Lincoln said he would enforce the fugitive slave law. I assume you would not call him a Neo-Nazi.
In early April 1861, an Illinois commissioner friend of Lincoln's in Springfield, Illinois, issued a warrant and ruled that some fugitive slaves caught in Chicago, a sanctuary city for fugitive slaves, should be returned to their owners. I've always suspected that Abe was pulling strings behind the curtain to make this happen to show the South he would enforce the fugitive slave law and live up to his word. Previous presidents had left Chicago alone. When this happened, the fugitive slaves living in Chicago made a mad dash for Canada. See the following three short New York Times articles about it: Link1, Link2, and Link3
The book, The Slave Catchers, subtitled Enforcement of the Fugitive Slave Law 1850-1860, by Stanley W. Campbell is a reasonably balanced book. The author points out on page 132 of the paperback version that "Because the federal courts did insist upon the supremacy of laws of the United States, these provisions of the personal liberty laws were ineffective in deterring enforcement of the Fugitive Slave Law by officers of the federal government." I imagine the federal courts were using the Supremacy Clause of the Constitution to rule against the state laws, well intentioned though those state laws might be. Here is a reminder of what the Supremacy Clause is: Link4. In other words, once the federal commissioners got involved and started enforcing federal law, state laws that conflicted with it were moot and unconstitutional.
The war and the issues surrounding it are more than one dimensional. I encourage you to stick around and partake in the discussion.
History grants us only a few recent examples of absolute evil -- the Nazi holocaust and Communist tyrannies come to mind, but also American slavery.
Of course you are free to argue the facts of history, such as constitutional sanctions and Supreme Court decisions (Dred Scott, etc.) legitimizing slavery.
But if you go further, to suggest that these are all good things and they morally justified such actions as Southern secession and war of rebellion, then you've gone too far -- and also make suspect your claim of defending black civil rights in the 1950s.
By the way, in the 1950s I lived in North Carolina for two years -- attended 3rd & 4th grade there. ;-)