"And if they send the same guys back, who are now deaf, they won't need any ear plugs at all."
And that's the point to be made. Our response (NOT .50) means they can come back. Are pirates bad guys or not? Why are we worried about their feelings? I'm sure loud noises would have discouraged the old, real pirates. Loud cannons without balls?
Think outside the box...it's not to keep from hurting the pirates. One reason it's non-lethal is to prevent having a lethal weapon that can be used in sitations other than an attack on the ship.