Why stop at one? Read them all. Read the speeches and the writings and the arguements made by the southern leaders and you will still find that I am correct. By far the single most often mentioned reason for the southern rebellion was defense of the institution of slavery against what they saw as a threat from the Republican administration.
Just for argument..........assuming this were true, it would impair the legality of secession and the moral and legal claims of the People to the right to rule themselves in sovereignty, how?