Sonic Weapon Used Against Pirates

From Boots & Sabers:

. . . a story about how a cruise ship, attacked by pirates off the coast of Somalia, used a non-lethal sonic weapon to drive off the pirates. Apparently, this weapon was developed by the Navy in the wake of the U.S.S. Cole attack.

We have only one question about this. If you want to drive off pirates (or terrorists) why should we care whether it’s a “non-lethal” weapon?