Michael, as an historian once told me, "they are what they are". Southerners knew the Republican platform (forget Lincoln for a moment) was to emancipate slaves without consent of slave owners. This would (and did) result in economic ruin and a sudden debut of 4 million poor black folks competing with poor white folks for survival. That political move was seen as a dire threat to the economic and social fabric of the entire South.
The Texas Declaration of Independence repeatedly chastises the federal government for being heavily biased towards Northern interests (and it was) and failing to provide protection against "savage Indians and murderous banditti) on the borders. That did not just include the Mexican border, but the west and North as well. The document reads explicitly that Texans were better off when they had a republic.
Some people, especially Yankees, will only look at these Declarations of Independence in 21st Century logic and 21st Century morals. You cannot make people think critically. Oftentimes, they don't have the ability.