Suppose I wish to express MY beliefs by preventing the public desecration of the flag, should I be prohibited by the government from doing so?
If you want to stand up and yell and talk about how great America is next to a guy burning a flag, sure, you can do that all you want.
If you want to punch him in the face, as you said earlier, you can do so at the risk of prosecution and a lawsuit.
We don't go around punching people because we don't like what they say.