Pirates only want the booty.
Emperors like the booty, too, but they sometimes unite people and create governments and institutions that protect and serve the people.
If pirates or marauders do the same, they cease to be pirates and transition to empire builders. See Genghis Khaaaaaaaaaaaaaaaaaaaan!.
I'm not for emperors or dictators, but you have to realize that pretty much all civilizations, kingdoms, and empires were founded by bloody wars and conquest. Only thing worse than living in a place ruled by a government is living in a place not ruled by a government (which, not-so-oddly enough, are where the majority of pirates tend to take refuge in).