Certainly, a pretty un-necessary bit of legislation.. a flag burner would necessarily want a crowd. The law of averages and current patriotic frevor considered..
..well, there's no law against stupidity, but as granpaw used ta say, "the penalty for stupidity is usually death."
On the other hand, some pretty good points have been made on the relative value of protecting the right of freedom of speech and expression and the infringement on those rights by frivolus legistaltion.
Net result.. no law needed.