Kind of simple really. Burning a cross is a symbol of hate, meant to incite more hatred. Burning the flag is a symbol of protest against what our country is doing. Of course, this is only in the US. And, God knows how often flag burning occurs. Cripes, one case of burning one in over two decades. If ever we needed that Constitutional Amendment...............
Thing is, crosses get burned way more often (statistics anyone?). And, they are not benign symbols of protest. However, do you see our fearless leaders putting together an amendment for that? Oh wait....... when this government becomes Christian, it just may come up. Nah, it's not about disdain for Christians; it's about hating people of color, usually black. Nah, no need to ban that via the Constitution. Nahhhhhhh......
In other countries, American flag burning is a symbol of hate, meant to incite more hatred. But, we have no control over that, do we? Well, I suppose if the neocons decide we should, they could just may start burning cities that condone American flag burning. Damn straight. Nuke 'em. Let God sort it out.