Some people try to take these Secession documents out of context and pretend that protecting slavery was the only issue for the South. Had slavery been abolished overnight without remuneration, the South would have been devastated economically and there would be mayhem in attempts at trying to assimilate newly freed black people in the society. Like Reconstruction, but worse.
Here is an excerpt from the Texas Ordinance of Secession that illustrates other issues.

By the disloyalty of the Northern States and their citizens and the imbecility of the Federal Government, infamous combinations of incendiaries and outlaws have been permitted in those States and the common territory of Kansas to trample upon the federal laws, to war upon the lives and property of Southern citizens in that territory, and finally, by violence and mob law to usurp the possession of the same as exclusively the property of the Northern States.

The Federal Government, while but partially under the control of these our unnatural and sectional enemies, has for years almost entirely failed to protect the lives and property of the people of Texas against the Indian savages on our border, and more recently against the murderous forays of banditti from the neighboring territory of Mexico; and when our State government has expended large amounts for such purpose, the Federal Government has refused reimbursement therefor, thus rendering our condition more insecure and harassing than it was during the existence of the Republic of Texas.