Try this little experiment sometime. Walk up to a large person and say "Hey, you're FAT." When they get angry and when other people within earshot start calling you an asshole, state that the 1st Amendment protects your right to call people fat. It does, after all. And since you're able to call people fat, doesn't it follow logically that you should?
This is an example I've been using in class for a decade to introduce the section on freedom of speech / expression when we cover the Constitution and Bill of Rights. What the 1st Amendment protects our right to say is almost without limit. Seriously, take a look through Federal court cases involving free expression. Then look around the internet at the things people say without sanction. You can find examples of every conceivable objectionable expression of ideas: racism, blatantly incorrect facts and history, websites dedicated to ad hominem attacks on single individuals or groups of people, misogyny, anti-anything groups, and so on. Hell, the average news site comment section is guaranteed to contain at least a handful of exhortations to kill somebody. Put on a Klan outfit and march around your city. Scream "Fuck you, Kikes!" as loud as you can in public. Start a group advocating the extermination of Muslims. People will think you're an asshole, but the fact remains that you can do any of these things legally in the U.S.
Of course you don't do any of them, because the fact that you can does not mean that you should or that you will. As a human being with a basic awareness of the society in which you live, it doesn't take much thought to conclude that these are all terrible ideas even if they did enter your mind for some reason.
OK? Let's talk about the Confederate flag now.
Can you plaster Confederate flags on your car, home, and person? Yes. You can do the same with swastikas, Juggalo logos, or images of Cap'n Crunch if you feel like it. It's highly unlikely that the Courts ever will interpret the 1st Amendment otherwise. If you want people to think you are a jackwagon, go ahead and do any of those things. Otherwise, consider these good examples of how discretion moderates your enjoyment of the rights afforded to you.
The important thing to remember, in that light, is that displaying the Confederate flag is not illegal but it most emphatically is a dick thing to do. When Mitt Romney, Jeb Bush, Rick Perry – Rick Perry! – and ultra right-wing Town Hall columnists say that it's time for the old Dukes of Hazzard flag to go, it's a pretty good sign that it is approaching swastika territory as the kind of symbol you're legally able to display but you might possibly probably be a major asshole if you do it.
As the aforementioned columnist states, "Like a lot of people below the Mason-Dixon Line – white people, anyway – I saw the emblem as a token of regional pride. I didn't revere slavery and Jim Crow. But I thought there was much about the South to love." You hear things like this a lot; it's a symbol of "southern pride", or honors the bravery of the Confederate soldier from 160 years ago, or heritage or tradition or blah blah blah. Try wearing a swastika t-shirt and telling curious onlookers that your purpose is to honor the memory of the Indus River Valley civilization of 3000 BC. They will look at you like you have brain damage or are in need of the padded van. So why should essentially the same argument hold any water with the flag?
It shouldn't. The Confederate States of America stood for "states' rights" alright – states' right to have slavery. If you want to honor your southern heritage, there are other symbols you could choose that don't stand for our racist past, the legacy of which fuels the racist present. You can choose symbols that aren't a giant, throbbing middle finger extended at about 30% of the population who are not white. Try your state flag. Try an image of your state or the whole south. Try literally anything that isn't a thinly veiled expression of semi-literate white underclass rage about the passing of the days in which they could stay off the bottom rung of the ladder simply by virtue of being white. Every time I see a Confederate flag I think of Gene Hackman in Mississippi Burning: "If you ain't better than a nigger, son, who are you better than?"
That's what the flag represents. So shut up about how you have the right to display it; you do. Spend a little more time thinking about whether it's a good idea. Think about what it says to other people. Think about what it says about you. When you get over your own stubborn ignorance you'll realize that it's not complicated. It's a very basic Can vs. Should problem with an obvious correct answer.