It certainly looks like the days of the Confederate battle flag flying on the grounds of the state house in Columbia, South Carolina are numbered. Th… - Brooks D. Simpson

Douglas would repeat what Lincoln said about racial equality at Charleston in debates to come, usually in support of his claim that Lincoln varied his remarks according to location. There was some truth to this, but far less truth to the ensuing charge of inconsistency. Douglas knew better, and by the time of the final debate, he had heard Lincoln’s explanation enough times. He simply chose not to accept it. He knew that when it came to Illinois voters, shifting the issue from slavery to race tilted the scales in his favor.

Ranting about "political correctness" is best read as "I can't really deal with the merits of your interpretation, so I'll deride it largely because it doesn't reinforce my own preferences and prejudices."

Once we understand that the flags in question are those of an army, we can have a more intelligent discussion about what those armies did, such as the fact that the Army of Northern Virginia was under orders to capture and send south supposed escaped slaves during that army's invasion of Pennsylvania in 1863.