I personally don't think the C.F. is relevant anymore. However, that being said, it was not a flag of a "slave nation". It was a battle flag of the Confederate Army. Not all southerners believed in slavery or felt the war was about slavery. To many it was about states' rights. Back at the time of the signing of the Declaration of Independence, there were many states that did not want to sign it. The fear was a centralized federal government would try and supersede the states' rights to set their own laws (which of course has now happened). Many felt Pres. Lincoln was over stepping the Constitution.
The C.F. represents a lot of different things to different people. It is probably not wise to hang it over any government building. It belongs more in a museum along with its true history.
The real issue here is 1st amendment liberty. I may not like you hanging your C.F. over your own home, but the constitution does not protect me from being offended by your 1st amendment rights.
Also, to blame the current racial discord on that flag is naive at best. The whole debate has been manufactured to stir up emotions and to divide our nation.