@miguelito21,
That the attitude of the southern states' political leaders didn't make sense is not a reasonable basis to object to the proposition. Ask yourself how often what politicians propose or actually do is based on good sense, and how often it is an appeal to popular prejudice, or an attempt to manipulate public opinion to serve the personal interests of the politicians and their cronies.
It also helps to understand the three-fifths compromise (look that up). That gave successfully manipulative politicians in the South enormous power, out of all proportion to their electoral success. The Missouri compromise of 1820 prohibited slave states north of 36 degrees 30 minutes north (with the exception of Missouri, which straddled that line, and which entered the union as one of pair, with Maine). Thereafter, states entered the union in pairs, one slave state and one free state. Southern politicians saw this as preserving their political power under the terms of the three-fifths compromise. It was assumed by southerners that this would apply to the new territories the United States acquired as a result of the Mexican War. However, the Missouri compromise didn't require states which entered south of the 36-30 line to be slave states, and another compromise in 1850 allowed California to enter the union, undivided as a free state. (Southern politicians had wanted it divided along the Missouri compromise line, one free and one slave state.) Part of the compromise involved New Mexico and Utah entering as slave states, although it soon became clear that the voting portion of their populations (white males) were not interested in slavery. Another part of the compromise of 1850 was a strong fugitive slave law, which experience soon taught southerners could not be enforced in the north.
Southern politicians saw their power under the three-fifths compromise being eroded, and rather than any of them sitting down and doing the math (math is hard!), hotter heads prevailed. Many southerners were convinced that it would be easy to win a war with the north (thinking realistically is hard!) and were contemptuous of the people of the north. "Pasty-faced mechanics" was a popular description of northerners used in the South. A lot of southerners wanted to go to war even before Lincoln was nominated, let alone elected--see the reference to John Floyd from my post above. Even after war had begun, southerners stared really hard at successful events, and dismissed southern military failures. People often believe what they want to believe.
It's probably not unreasonable to suggest that many secession votes were fiddled. Whether or not, just as a great many people today who are not wealthy, and never likely to be wealthy nevertheless support tax cuts for the wealthy because they dream of someday being wealthy, or that their children will be wealthy--so there were many people in the South who were not slave-owners, and were never likely to be slave owners, but who dreamed of being slave owners or of their children being slave-owners. This gave the slave-owning political elite power beyond their numbers. Nevertheless, after the initial rush of volunteers, the Confederacy could not meet their manpower quotas, and the Confederate States instituted conscription well before it was done in the North. Support for slavery was not a monolith, and desertions from Confederate ranks were such a problem that many commanders--Thomas "Stonewall" Jackson is a notable example--proposed that their soldiers should not be given leave. Far too many of them used leave as an opportunity to desert. The western counties of Virginia seceded from Virginia, and in 1863, the state of West Virginia was created. (That vote was probably fiddled, too, in favor of secession from Virginia.) Eastern Tennessee remained a Union stronghold, and Knoxville successfully withstood long sieges by southern armies, even including one by Longstreet conducted in late 1863. Lincoln's second running mate, Andrew Johnson, was from eastern Tennessee. Support for the Union was not a monolith either, but union support held up better than the support for the Confederacy.
Basically, southern hotheads were hell bent on war in 1860, even before Lincoln was elected. Lincoln did not take office until March, 1861, and the war had already begun by then.
The tariff was a divisive issue, but it didn't lead to war. What we now call states' rights was a divisive issue, but it didn't lead to war. (Look up nullification and the nullification crisis of 1832.) Everyone would have been economically better off with the tariff, even in the South--but, once again, common sense does not necessarily prevail in politics. As early as 1758, before the French and Indian War had ended, Washington realized they were getting screwed by their European agents, and he stopped growing tobacco on a large scale, diversified, and stopped buying his goods from agents in London. He then took the austerity measures necessary to pay off his debts and the debts entailed on his half-brother's estate, Mount Vernon. The tariff actually only threatened the convenience of southern planters. They had wharves on the rivers that lead into the interior, and small sailing ships could sail upriver, tie up at the wharf and load the tobacco or cotton to be sold in Europe (mostly in England). The goods they had ordered the previous year would be delivered at the same time. They were getting screwed twice. Factors (agents) in England could report any price they liked as what they had gotten for the tobacco crop which had been shipped the previous year, and the records show they robbed their customers shamelessly. They could also, and almost ways did, provide shoddy goods at premium prices. The big planters were actually getting robbed on a routine and traditional basis, and the was no hope at all for the little guy.
I can actually go on for pages on the subject of the myth that American prosperity was based on slavery. Rather than do that, though, i'll just state that the United States prospered despite slavery, not because of it. I've already covered this subject in this thread.
I have other things to do. If i remember, i'll come back to address the issue of why the preseveration of the union was so important. That won't take long.