While it may be true that the precipitating reason for the Confederate States to secede from the Union was slavery, the war aim of Washington initially, and for several years after the war had started, was not to end slavery, it was to "preserve the union". That was specifically stated by Lincoln.

And yet it is by no means clear that there is not an implicit right of secession in any federation. Thomas Jefferson seems to have believed there was: "If any state in the Union will declare that it prefers separation ... to a continuance in the union .... I have no hesitation in saying, 'Let us separate.'"

Loading all the guilt for slavery and racism symbolically on the Confederate flag, and implying that the Union flag (in its various adjustments over the years) does not share that symbolic guilt, is to distort history and involves a failure in some ways to face up to that history, which is a "shared history". Both flags have been flown at lynchings.

Flags are strange and dangerous cultural artefacts. If it is possible to retrieve them from those who would use them to propagate hate and prejudice, is that such a bad idea? In the UK the Confederate Flag is generally seen essentially as the regional flag of the South, in the context of music. I'd see that as positive.