Here is the simple answer: The South relied on agriculture to survive economically. It relied on cotton because it was easy to grow and there was a great demand for it. In order to earn money off these crops, though, the South needed cheap workers that could plant the cotton. Slaves were the "perfect" solution.
It was the mainstay of their only major industry - cotton. Profit was so minimal that it would have destroyed most the farms in the South. It was called the necessary evil. Also it was easier to take care of slaves than to pay them a descent wage. After slavery was abolished some stayed on the farms receiving a piece of land from the farm to grow their own crops while bringing in the crops for their new employer.
Because the plantation owners had invested a lot of money in buying their slaves and didn't want to see the slaves free to leave.
Because Lincoln would not allow any extension of slavery
what did many white southerners do to try and stop the movement
take power away from the southern planters.
they felt it was important because people felt they didn't have to do Manuel labor
Paternalism
...that slavery should not be abolish
because many southerners disagreed with lincoln because he had spoken out against slavery
The Mexican government offered them land and they could have slavery.
Many pro-Union Southerners kept the North informed of supply caches to provide targets for the Northern army. In addition, these Southerners withheld financial support to the South.
because southerners thought Abraham Lincoln was going to remove slavery
The vast majority of white Southerners could not afford slaves and struggled for basic self-sufficiency.
They didn't have much economic opportunity in the old South.