UChessmaster made an excellent and valid point, though: It'd be strange if the marines don't capture any pirates during this confrontation, assuming the whole place won't get levelled and the pirates win. But that seems somewhat dubious. Looking back at this whole operation, I don't think the Whitebeards demonstrated overly good planning and strategy all in all. It would be strange if their escape plan, then, would be so excellent that every lowly deck scrubber gets away.

From a strategic point of view saving a man of Ace's calibre and standing (an officer, to use military terms) is of course much more important than saving some nameless thug. Also, like has been said before, what would their whole army stand for if not for taking action when action is needed? It's no cold war since nobody has Plutons or other doomsday machines.

Edit: The next one to continue the stupid trolling war gets an extra vacation. Grow up, dudes. In this world you won't always get the last word.