This is a strange conclusion.
Through the normal Constitutional Political process, maintenance of slavery was the one thing that was undoubtedly and rigidly safe within the Union. It would appear as though the Radicals were the ones who used the war to circumvent the process.
Maintenance of slavery was not the main issue dividing North and South in 1860, expansion of slavery was. There was a big difference.
It's a regret that there was not enough people in the South with your viewpoint in 1861 because we wouldn't have had this statement from the South Carolina declaration of causes for secession:
"A geographical line has been drawn across the Union, and all the States north of that line have united in the election of a man to the high office of President of the United States, whose opinions and purposes are hostile to slavery. He is to be entrusted with the administration of the common Government, because he has declared that that "Government cannot endure permanently half slave, half free," and that the public mind must rest in the belief that slavery is in the course of ultimate extinction."
The words of the Confederates of 1861 plainly point to slavery as the central issue.