See I loved Lynyrd Skynyrd. And I love Tom Petty, and he used them for his "Rebels" song and tour about 30 years ago. Also it's important to remember that what we think of as the Confederate flag was actually the flag of General Lee's Army of Northern Virginia (the main Confederate army in the east.) The actual flag of the Confederacy, known as the "Stars and Bars" is a very different design. The Army of Northern Virginia was heroic, and celebrating this particular flag, it can be argued, doesn't so much celebrate slavery as it does the battles that Lee's Army fought.
That being said, we have now reached a point in our history in which anyone who displays this flag HAS to be aware of how offensive it is to African-Americans. Even 30 years ago that was a question in debate; it's not anymore. Displaying the flag on cars and other public places, or on clothing, is being deliberately rude. It shouldn't be illegal IMO. But it also shouldn't be part of a license plate which the state manufactures.