You're not wrong, but it's a secondary issue in the context of contemporary civil rights. As a white man, the endorsement of slavery in that flag offends me but doesn't frighten me. However, as a Northerner, the display of the Confederate flag by a Southerner communicates to me that they could shoot me, in defense of things up to and including the utterly loathesome, if it suited them. I wouldn't expect a 21st-Century Southerner to endorse slavery, per se, but rather that "celebrating their heritage" includes - not just coincidentally, but specifically - killing people like me. Like I say, I'm willing to have my own concerns take a back seat to those of black people when it comes to issues surrounding the display of the Confederate flag. But if we can allow ourselves to have a list of issues longer than 1 item, those flags are an undisguised "up yours" to everyone north of Virginia, and I don't think I would feel very welcome in the South.