Slavery was headed for economic extinction anyway. There was no need to fight a war over it.
Tell that to the leaders of the confederacy.
"[Slavery] was established by decree of Almighty God...it is sanctioned in the Bible, in both Testaments, from Genesis to Revelation...it has existed in all ages, has been found among the people of the highest civilization, and in nations of the highest proficiency in the arts." Jefferson Davis, President of the Confederate States of America.
"Jefferson Davis, Constitutionalist: His Letters, Papers and Speeches. J. J. Little & Ives Company, 1923, Page 286.
"When you reach the end of your rope, tie a knot and hang on." — Abraham Lincoln
Your original quote was in error....
“Tell that to the leaders of the confederacy.”
The Leaders of the Confederacy were wrong about a lot of things.