As Americans, we have little to beat ourselves up about regarding slavery. It has existed literally everywhere, virtually since the dawn of man.
Most enslaved others for many hundreds, often thousands of years. Indeed, many continue even today.
By comparison, slavery only existed under the US flag for 80 years; and under the Confederate flag for 4 years.
By any comparison, the US should carry very little shame about slavery.....and the 'South' even 20 times less than that.
Slavery was the defining characteristic of the South and led to its rise and fall. Americans who fought against slavery and who take pains not to glorify the Slavers have no reason to apologize. Democrats on the other hand have plenty to apologize for including the 100 year reign of racism following the Slaverocracy's defeat.