Pirates are meant for FFA games, where they can be used to keep one player busy while you attack another. In 1v1 they break the game (getting two pirate raids in a row on your opponent is probably game over), while in larger games they are irrelevent (oh no, pirates are attacking one planet of one player in an 80 planet game). Ironclad has NEVER managed to nail the balance on them, and probably never will unless they change the ebay system.
I strongly suggest any new players turn them off, only adding them in if you know what you're doing.