"Lincoln's refutation of secession as a constitutional right rested entirely upon the truth of the doctrine that the just powers of government are derived from the consent of the governed. That, according to Lincoln, was the 'sheet anchor' of the republican form of government embodied in the constitution and guaranteed by it to the states. 'We the people' possessed the authority to ordain and establish the Constitution, because those who ratified it had been endowed by their Creator with certain unalienable rights. Those rights entitle any people to alter or abolish any government that does not secure those rights and institute a government that, in their judgment, will do so and thereby provide for their safety and happiness. Those rights were the reason or reasons informing the authority of 'We the people' and the ground of the republican form of government. The moral rightness of republican government was moreover identical, in principle, with the moral wrongness of slavery. Republican government could not be right unless slavery were wrong.
"The rights of man were both natural and divine. they possessed their authority from God and nature. They were knowable by the exercise of unassisted reason and were the heritage of all men everywhere...
"According to Alexander Stephen's Cornerstone speech in 1861, the natural rights philosophy of the Founding Fathers had been replaced in all scientifically enlightened minds by the doctrine of racial inequality. Stephens never expounded the new 'science,' but it may be assumed that a decisive contributor to that science was John C. Calhoun. There can be no doubt that it was Calhoun who supplied the 'ingenious sophism' that had 'sugar coated' rebellion and brought the public mind of the South to believe that secession was a constitutional right."
Harry Jaffa, A New Birth of Freedom
"However strong a government may be, it cannot easily escape from the consequences of a principle which it has once admitted as the foundation of its constitution. The Union was formed by the voluntary agreement of the states; and these, in uniting together, have not forfeited their sovereignty, nor have they been reduced to the condition of one and the same people. If one of the states chose to withdraw its name from the contract, it would be difficult to disprove its right of doing so, and the Federal government would have no means of maintaining its claims directly, either by force or by right."
Put another way, to deny voluntary secession is to deny the principle of consent upon which the similarly voluntary union was founded. If you deny that principle then the union built on it is rendered illegitimate. And yes, I'll take Tocqueville over a Lincoln-worshipping illogical gasbag from Claremont any day.