You are missing the mark. It was "tolerated" in the 19th century because it was almost universally understood that the black race could not survive on their own. They were deemed incapable of succeeding in a capitalist society, they could not be educated. Sorry, that's the ugly truth. They were thought of as children. Who would want to emancipate a child with the abilities of a 10 Y.O.?
Tolerated is the correct verb, at least among the Founders’ generation. Many of the Founders were well aware that slavery was morally wrong. Most believed that it should be ended. However economics and factionalism prevented them from doing more to end it. By the time of the Civil War, the system was so entrenched in the Southern economy that there was no hope of voluntary abolition. It is true that Southerners argued for slavery as a positive good, but at least IMO, that was in response to the moral arguments that the abolition movement put forth. Without the economic basis slavery would probably have disappeared. Certainly people in the North, despite the overly simplistic understanding of the Civil War currently prevalent, were not more morally enlightened than those in the South. Northerners, even most abolitionists, would never have favored equality for Black people. Why then was slavery eliminated in the North long before the war? Simple economics, the industrial economy worked better with paid labor.