And what about the consequences? The civilians killed have families, so do the marines. Just as a kid losing his parents to pirates would lead him to become a marine, a marine that kills his parents in pursuit of a pirate will probably be lead to become a pirate himself or even worse. Because if the justice and the law of the world he lives in is one that uses pirates as an excuse for their own crimes, one that will condemn them just for being in the vicinity of a pirate even if they didn't know it and will label them as criminals, then they may as well live against it from the start. You can't be sure that fighting along with him will save lives either.