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.
I'm wondering if you are aware that at the time of this nation's founding (July 4, 1776) every single state was a slave state?
Thomas Jefferson's efforts to introduce anti-slavery commentary into the Declaration were rejected and overridden by the other members of the committee because that would have blown apart the coalition before it even tried to form.
So "Tolerated" isn't quite right. "Accepted with misgivings" is probably more accurate.