It's Always About Money

The Confederate flag became a symbol of hate when it was used by General Lee in the civil war.

A war, from the perspective of the South, about the economic impact the South would be forced to endure by losing the free labor of slaves or more simply put money, and the perspective of the North human rights. (Not to suggest that the North was much further along in their views.)

It was never accepted or used as a flag of the collective South until well after the failure of their secession. (Note that even General Lee declined this or any flag be flown at his on funeral) Later, during the Civil Right movement, angry white trash supremists started thinking they needed to shift the blame of their inferior social and financial well being from their mental inferiority to a racial issue and boo hoo about victim status. 

How? Strom Thurman used it during his campaign for presidency as a unifying symbol for people who stood for racial segragation.

There's no way around it though, unlike the Nazi's adoption of the swastika which had been used throughout history in various cultures and languages to mean a myriad of other things, the "Confederate" flag was always meant to represent slavery and racial division/hate.

All that said, the support of its display as being based in any sort of historical context only further exemplifies the ignorance that perpetuates hate.