Well, if the South "never did 'abandon'" its beliefs "about slavery," that would mean you think the South STILL believes it now!!! Utter ludicrous comment!
You might try reading a paragraph instead of a sentence.
The South did not voluntarily abandon slavery because they had stopped believing in it. It was imposed on them by force of arms.
By a short time after the war, most southerners were willing to agree that slavery had been wrong, but they didn’t give it up because they were convinced of this, but rather became convinced after they had been forced to give it up.
The South was forced to abandon slavery much the way Mormonism was forced to abandon polygamy. Irresistible political and military force.