The AP: Pentagon chief endorses call to cancel Quran burn
The burning of symbols such as flags, books, and garb is one of the purest forms of free speech.
It is not to be regulated or stopped by any government action.
Aside from the fact that it's legal, it's a negative way to build support for your cause, by destroying symbols of that which you oppose, instead of doing something positive like building more symbols of what you support. People want to be positive, not negative.
Obviously, this is an action meant to create a reaction that will be so unequal as to draw further opposition to the target. Whether this course of action will be judged in hindsight to be worth it, will probably depend on the feelings of the headless torso that will likely result.