When seen through the lens of states’ rights, it is easy to defend the Confederacy and the monuments. Slavery is a separate issue; a couple of slave states fought for the North, and all of them had slavery at some point (it was outlawed in my state of NJ 15 years before the Civil War), so the Union flag should be just as offensive.
If they want to re-write or erase history, let them be thorough (not selective); get rid of the stars & stripes.