They would have been just as opposed to Stephen Douglas since he was not fanatically pro-slavery enough for the Slavers. In fact, the reason Lincoln won (38% of the pv) was because the aristocratic southern lunatics refused to support Douglas and split the RAT party into three parts each with its own candidate. True lunacy if there ever was such.
The leading candidate for nomination by the democratic party as President was Stephen Douglas of Illinois. By this time, many informed Southern politicians were wise to Douglas. They knew that he had sold out the transcontinental railroad route through Louisiana and Texas for worthless concessions in the Kansas-Nebraska Act. They knew that Douglas preached a program desired by financiers in Philadelphia and New York. Such was the main bone of contention which this faction of Southern politicians had with Douglas.It was increasingly obvious to thinking men in the South that geography barred their peculiar institution in the Federal territories. No amount of argument can change the unanswerable reality that, outside of Kansas where they were doomed before they started, planters from the Dixie States had made no serious effort to import slaves into the huge land mass affected by Compromise of 1850 and the repeal of the Missouri Compromise in 1854. They made no serious effort, because there was nothing attractive to them in those vast stretches. And the proof of this stubborn fact is that in 1860 there were no slaves at all in the New Mexico, Utah, and Washington Territories, none in the Indian or Oklahoma Territory, none in the Dakota Territory, virtually none in the Kansas Territory which entered the Union as a free State in 1861, and barely more than a dozen in the Nebraska Territory, nor was there a prospect that more would ever arrive.
The burning issue for Southern democrats was the transcontinental railroad, because it would have been of great value to their region of the United States as a stimulus to modernize their economy and society, and thereby to help phase out slavery.
Actually a cynical political calculation. The radical in the South understood that they would never get popular support for secession unless a "Black" Republican should win. They intentionally split the Democrats to assure a Republican win and therefore attain their goal -- splitting the Union.
They had propagandized the southern people with stories that would make Michael Moore blush about how the Republicans would have the slaves become the masters and black men raping their wives and daughters. Crude, but it worked --- for a time.