Blaming others for our failures is not an attribute to be sought. The professing Christians who first settled America tolerated slavery. But, as time went on, and the true nature of the abomination became better known (Uncle Tom's Cabin) there was a sea change among those who held no or very few slaves. Eventually the reality of the brotherhood in Christ made slavery untenable. For example, try reading Philemon.
So one message of the needless monuments is that people (southern pastors) could turn scripture into something that tolerated slavery. We have multiple posters here who deny the very essence of the civil war. But the Bible is crystal, we are to treat our neighbors (black and white, yellow and brown, and all the mixtures) as we want others to treat us. Shackles anyone?
Last point, if you have not seen "Amazing Grace" take some time and view it.