The thing about flags and other symbols is that their interpreted meaning is not static. The common understanding of a symbol can change drastically due to association with new groups and people. For instance, the Nazis did it with more than just the swastika. You know that SS emblem with the S characters that look sorta like lightning bolts, the insignia of the Schutzstaffel? Those are taken from runic alphabets that were used all over Europe before the Roman alphabet took over, this specific one being a version of the
sowilo (sun) rune. Now if you throw two of those things together, instead of it meaning "sun sun" (for a shitty literal translation, of course) it would for most people become a reference to the Nazi SS and the things they did.
This is simply how the human mind works. A symbol is used in association with something good or bad, so we attribute those good or bad things to the symbol. That is why two overlapping lines, one relatively short and the other relatively long, arranged in a particular way can bring to mind Christianity and everything associated with it instead of just looking like a lowercase letter T. That is why two overlapping triangles can do the same for bringing to mind Judaism and the Jewish people instead of just being a geometric pattering. That is why the star and crescent symbol makes most people think of Islam rather than the Ottoman Empire that used it as their flag. The flag that people want taken down from South Carolina's capitol building has a long history of negative associations: slavery and war thanks to its origins, opposition to civil rights thanks to its use by groups opposing the civil rights movement of the 1940s, and general racism and racial violence thanks to its use by all sorts of racist and white supremacist groups. Ignoring that history to claim that it stands for none of those things would be to ignore how symbols and the human mind actually work.
If you want a flag to commemorate the history and pride and such of the Confederacy without people raging at you, then use their original national flag, the
Stars and Bars, because that one doesn't have all the baggage that the Confederate battle flag does. By the way, that flag everyone just calls the "Confederate flag" was never actually the national flag of the Confederate States of America, and in fact it was originally just the flag used by the Army of Northern Virginia. It was adopted as a battle flag because the Stars and Bars looked far too similar to the Union flag from a distance. It was then adapted as part of a new national flag in 1863, plain white with the battle flag as a canton (a red stripe was added on the right side of the flag a couple months before the war ended), but the plain old battle flag was never the official flag of the Confederacy.
All that said, I don't give much of a fuck about this particular instance of the Confederate battle flag being used. It's on a war memorial for dead Confederate soldiers; that is one of the few places that it really makes sense to display that flag, some other examples being museums and Civil War reenactment things. If people want it removed, whatever, remove it. If people want it to stay, whatever, let it stay. It should be up to local people who actually might see the thing once in a while, not the waves of public outrage from people who have probably never even set foot in South Carolina.