The greater damage to the nation, imo, came not so much from the Founders compromising with Southern slaveowner demands in the Constitution, but from the North backing off during Reconstruction after the Civil War and allowing the South to essentially write the narrative of the war, and allowing Southern states to pass Jim Crow laws and effectively return Southern blacks to a state of near-slavery for decades. The North had won the war, the white South was on its knees, and yet the North eventually gave up trying to protect the rights of Southern blacks by 1877.
The narrative of the Civil War that was used in history textbooks for decades, even outside the South, downplayed the role of slavery in causing the war, depicted slaves as being generally happy and content with their condition and well-treated by Southern slaveowners, and often depicted the Confederates as heroic underdogs who were just overwhelmed by Union might (virtually no mention was given to the tens of thousands of black soldiers who served in the Union Army during the war, or to the elected black Southern politicians after the war), and men like Robert E. Lee were depicted as anti-slavery and anti-secession, even though they somehow managed to fight fiercely for four years for both slavery and secession. That narrative of the heroic underdog white South resisting the overbearing, overwhelming power of the US Government (basically the Galactic Empire), persists among many whites to this day. The actual causes of the war, how slaves really felt about their condition, the real motivations of men like Robert E. Lee and Stonewall Jackson (as opposed to the myths), and so on, is just foreign to these people. The South lost the war, but won Reconstruction and setting the narrative of slavery and what caused the conflict, the role of blacks during and after the war, and so on, and that victory continues to haunt the nation to this day.