Lincoln couldn’t have been more clear that he would protect slavery and even strengthen fugitive slave legislation. Slavery was not threatened.
We can debate part of that but is still doesn't change the fact that the Southern states seceded long before Lincoln was inaugurated and adopted a constitution that protected slavery to a far greater extent than the U.S. Constitution did, even had the Corwin Amendment been adopted. They were motivated to act out of a sense that their institution of slavery was threatened by the Lincoln election.