clearly protected by the first amendment and indeed has been ruled so by the courts. Who fought and died for it is not relevant (in fact I would argue they weren't fighting and dying for a piece of colored cloth). Like the national anthem, it doesn't belong to the military. Burning it isn't something I would take lightly and if I chose to do it I would have a reason, the primary one being if I thought that the United States were abandoning its ideals or the rule of law. But it is a really "in your face" action.

By the same token, flying the Confederate flag is also an "in your face" action. Since it seems to concern you, a lot of the people who fought and died for the US flag (or really its ideals) had to do so to put down a rebellion represented by the Stars and Bars and the Confederate battle flag. It sure seems to be held in reverence though by people claiming to be patriots.