not to mention generally the guard is usually attached to either the lense itself or the mounting points for the light, so if you strengthen the light itself, you end up breaking the part it mounts to, in this case the flare. something has to give.
I feel the same way about the tail light guards there are 2 kinds. one type attaches to the screws that hold the lense on the housing WTH good is that gonna do, if you hit something it will just break the housing instead of the lense. the other style bolts to the tub behind the light, but as we all know the tub sheet metal is very thin, and I think I would rather break the housing or crack the lense, if it could possibly avoid caving in the tub.