When people refer to “the Confederate flag” most are thinking of the battle flag, also known as the Southern Cross, that was originally said to embody “the destiny of the Southern master and his African slave.”
The second official flag of the Confederacy, known as the Stainless Banner, put the Southern Cross in the upper left hand corner of a white field.
The designer, W. T. Thompson, said his design symbolized the Confederacy's ideology of “a superior race.” But Thompson’s flag didn’t last because the large white field made it look like a flag of surrender if the wind was blowing the wrong way. It was modified by adding a large red stripe on the end of the white field and was then called the Blood Stained Banner.
Long after the Civil War, the Southern Cross — the battle flag, the rebel flag — has come to represent in the minds of some The Cause of the Confederacy — which they like to think means standing up for states rights. But as a group of Southern political scientists wrote in their book Confederate Symbols in the Contemporary South:
"The battle flag was never adopted by the Confederate Congress, never flew over any state capitols during the Confederacy, and was never officially used by Confederate veterans' groups. The flag probably would have been relegated to Civil War museums if it had not been resurrected by the resurgent KKK and used by Southern Dixiecrats during the 1948 presidential election."
So when anyone says they display the rebel flag as a celebration of heritage, not hate, that heritage is inextricably tied to armed rebellion against the United States in the cause of white supremacy and slavery. Which is also known as racism.