The US Code provides that it is illegal to burn the flag, but the United States Supreme Court has held, several times, that burning the flag is a protected form of speech.
If you think about it, it really is speech. Which is why burning the flag is so controversial. When one sees the flag burning, it is not just a piece of cloth, it is a representation of the American country and its values.
Those who would support a constitutional amendment to protect the flag believe that the symbol is sancrosanct, and that there is never a justification for it.
Those who oppose it believe that, while it is just cloth, the burning of the flag is the strongest possible statement that America's values (like the flag) have gone up in flames, and that the leaders no longer stand for the values made dear by the country and its framers.
In any event, at least for now, you cannot be arrested for burning the flag (absent some other violation).
