Where do people get the idea that the US is a "Permanent" Union, because it just isn't so. Nowhere in the US Constitution does it state or even imply this. Notwithstanding the 1869 ruling in Texas Vs. White, which the Supreme Court ruled that states could not unilaterally secede from the United States, the Constitution DOES NOT EXPRESSLY FORBID SECESSION. And it never has.
I'm sure it would offend many a black individuals and many whites too, to learn that slavery was an institution that until the 13 Amendment, was permitted and protected by the FEDERAL Government.
I am also certain it would shock untold millions that the "Great Emancipator" had this to say about the Corwin Amendment (if you don't know what that is, look it up), to which he replied: "I understand a proposed amendment to the Constitution . . . has passed Congress, to the effect that the Federal Government shall never interfere with the domestic institutions of the States, including that of persons held to service. I have no objection to its being made express and irrevocable." And I believe it would shock them even further to learn that also Lincoln espoused freedom for slaves and hatred of the institution of slavery, he had this to say in 1858: "I will say then that I am not, nor ever have been in favor of bringing about in any way the social and political equality of the white and black races, that I am not nor ever have been in favor of making voters or jurors of Negroes, nor of qualifying them to hold office, nor to intermarry with white people; and I will say in addition to this that there is a physical difference between the white and black races which I believe will for ever forbid the two races living together on terms of social and political equality. And inasmuch as they cannot so live, while they do remain together there must be the position of superior and inferior, and I as much as any other man am in favor of having the superior position assigned to the white race."
We as 21st century people cannot and will never understand what was in the 19th century minds of our fore-fathers. What we see as base, horrible, and completely immoral today was commonplace then.