Do you have any support for this assertion?
(Lincoln was mean, etc. etc.)
I note with dismay that I have repeatedly posted an inquiry as to what "rights" the South seceded over in 1860 if not the right to hold slaves. You have noted that the Founders felt a balance of power was important between the federal government and the states, which is undoubtedly true. You have noted that the Southern states felt that they had the right to secede from the Union, which is also undoubtedly true.
To say that the Southern states seceded in order to demonstrate their right to secede is however both a logical absurdity and unsupported by the actual secession resolutions themselves. To say that the Southern states seceded in order to protect their "rights" makes more sense, but the question is then what these rights are. If these rights are to "the right to live free from federal tyranny", then the question becomes in what way the federal government was acting tyrannically towards them, that caused the South to secede in 1860 instead of 1859 or 1790.
The truth, as can be evinced from both history and the secession resolutions, is that the South wished to protect its right to practice slavery, and the reason why it felt the need to secede to do this was because in 1860 a President was elected who was pledged to stop the expansion of slavery into new territories, which would diminish its viability as an economic institution. The South had successfully made slavery the "third rail" of American politics in the years before the war; the Kansas-Nebraska Act which overturned the Missouri Compromise was an attempt to bolster slavery, as was the "gag rule" which forbade Congressional debate about abolition. Historians have pointed to the Mexican War as another Southern adventure to expand slavery (although this is an entirely different topic). When a President committed to a free soil policy was elected, the Southern states felt that the jig was up and seceded to protect their right to the "peculiar institution".
As the Mississippi secession declaration demonstrated, behind the pious handwaving about the South's right to protect its culture and sovereign destiny, "[their] position is thoroughly identified with the institution of slavery -- the greatest material interest of the world."
In the end, the only federal tyranny the South was fleeing was the possibility that slavery and its expansion might be threatened, and the shaky reasoning that "slavery is in the Constitution, and the North is opposed to slavery, therefore the North is opposed to the Constitution" is the root of Southerners' bleating that they were seceding to protect slavery and two states' rights to be named later. Many honorable men followed their states into secession and bemoaned the South's aggression against the federal United States, but the real face of the Confederacy was Bully Brooks, not Robert E. Lee.
You asked why the South seceded if it wasn't over slavery here is your answer - (Note slavery is mentioned, but it isn't the main reason if you look at them as a whole)
1. Our States entered the Union with the understanding that they had the right to withdraw when membership proved unhappy.
2. We were tired of being gypped by unfair tariff laws. (That started in 1788 when the Northern States by act of Congress shifted the burden of their fair share of the debt for the War of Independence on to the Southern States, and then on through protecticve tariff enactments that favored the Northern States at the expense of the South).
3. We were fed up with insane abuse from South-hating fanatics. Harriet Beecher Stowe (a New Englander who never visited the South in her lifetime) and John Brown, and the Abolitionists who all took pains to incite Southern slaves to rise against their masters. They poured torrents of abuse on the slave owners by putting out the story of Southern Plantation owners being infamously immoral. They (the Abolitionists) denounced the membership of a certain group of Southern churches as "incarnate fiends", "endorsers of crime of depraved humanity." One enthusiast wrote that Southern men came North to find wives because of fear that Southern girls were unworthy. (A patent falsehood!)
4. We bought our slaves from the North, only to learn later that it proposed to free them without a penny of compensation.
5. Northern fanatics had inspired murderous slave-uprisings. Why wait for more?
6. A rabidly-sectional party was in control at Washington.
7. We had no idea of making war. We planned to relieve the North from further association with us.
Lest you conclude that only Southerners believed they had the right to go their own way and be let alone, bear in mind the view of Henry Cabot Lodge, a New England Brahmin. He said as of the date of the adoption of the Constitution, it waws universally regarded as an experiment, entered upon by the States, and from which any State had the right to peaceably withdraw.