Slavery was certainly a prominent issue at the time, and the Declarations of Secession you posted point that out well enough. That said, the fear that Lincoln would free slaves could well be described as the straw that broke the camel's back. There had been tension for decades prior, and there was serious talk of secession around 1850. Had that happened the outcome would quite likely have been different since the north wasn't quite the industrial might they were a decade later.
Relatively few southerners owned slaves, so it's obvious most foot soldiers weren't simply fighting for that right. What many don't realize is that while Lincoln freed the southern slaves (in token) in 1863, slaves in northern states weren't freed until Dec. of 1865 whereas southern slaves were free when the war ended (except in Texas). In the end, money was a primary reason for the war, and that's on both sides.
Normally I don't copy and paste very damn often, but time is short, and, since historians have documented so much and so well, I thought it reasonable to do so here. Following are some of the reasons for the conflict from a southern point of view. This certainly isn't a complete list, but it provides quite a bit of insight into the things that eventually led to secession. The idea didn't suddenly spring up overnight with the election of Lincoln, and the north wasn't some grand bastion of freedom for blacks. It's certainly difficult for us now to understand the mindset of people of that time, and it's even more difficult to understand how anyone could advocate owning another human being, but it was indeed a different time. People had a very different point of reference then, and to simplify their reasons for monumental decisions to a single factor that is popular today doesn't do history justice.
For more than 40 years Southerners spoke of "disunion" over a variety of issues. By the time Abraham Lincoln was elected president a single issue, the rise of the abolitionists, became the focal point of Southerners.
Tariffs levied in 1816 were aimed at lucrative Southern markets. Many Northern politicians were looking at wealthy plantation owners and wanting to share that wealth with their constituents and tariffs were the means by which to accomplish this goal. Protectionist fervor, fanned by pre-1816 success creating industrial growth through the Embargo Act was somewhat muted by shippers and merchants who opposed tariffs, but in 1820 and 1824 the United States once again was trying to increase tariffs.
The Tariff of 1828 precipitated the first secessionist crisis, in South Carolina in 1832. The battle pitted Vice-President John C. Calhoun against President Andy Jackson, ending with the Nullification Crisis. Luckily, another compromise was reached, courtesy of Henry Clay, and the crisis was avoided. Part of the compromise included a roll-back of tariffs to the 1816 levels over a 10-year period.
When the period was up, however, the pro-Tariff Whigs decided to reapply them to pay for their "internal improvements." The only problem was these internal improvements benefited Northern shipping interests and Western land speculators and not the South. For example, lighthouses had always been state-owned and run. The Northern shipping magnates wanted more lighthouses in the South and when state governments said no, they simply nationalized existing lighthouses and began increasing the number with the tariffs. Tariffs are generally considered to be a "Lost Cause" of the Civil War, but the cited example is directly out of the Georgia Causes of Secession document.
Expansion of government powers
Thomas Jefferson knew as President he did not have the power within the Constitution to agree to buy Louisiana from the French, but he did it anyway. This single act set the stage for a major shift in the political power in the United States, away from the states and to the President and Congress. The South felt that the President and Congress only had powers specifically granted them in the Constitution, but northern and western interests wanted a government who would do more for them and favored expansion of these powers. Even the federal judiciary got in the act, extending its authority over the province of state courts, again reducing the power of the states (Martin v. Hunter's Lessee (1816) and Cohens v. Virginia (1821).
Politicians, Northern and Southern, were generally labelled "strict constructionist" or "loose constructionist" based on their concept of how closely the Constitution should be followed in determining the power of the federal government.
"The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people" is directly from the Bill of Rights.
In the early 1850's states rights arguments faded, but by the end of the decade Southerners talking disunion were talking states rights, hardly the "Lost Cause" some want to make it out to be. The South got support from some unusual places: Wisconsin defended the sovereignty of the state in 1859, albeit over sentences imposed under the fugitive slave law.
“Which way General?” the aide asked. “Either,” Forrest growled. “If one road led to Hell and the other to Mexico, I would be indifferent which to take.”