Pirates were basically a manifestation of rebellion against an abusive and corrupt system.
The Navy could kidnap you off the street and force you to enlist, or merchant ships could take you and withhold wages and give shit terms to force you to work. And the living conditions of a sailor were pretty terrible.
Pirates said "fuck that" and created their own system.
Granted, pirates were terrible people most of the time. And alliances and marks and the countries they would prey upon were more complicated than "grr society bad". But as an instance of revolt/revolution they are incredibly interesting. They werent some random abberance in society, they were a central threat to and factor the Western World's economy at the time. As well as a handy force to be utilized by nations in the form of Privateers.
They had small parts of the world carved out for themselves, and some were involved in the politics of the time. (Such as the struggle between the Scots and the Brits for their king).
Ninjas are cool, too. But everything that makes them cool is basically myth. They were mostly low class peasants that operated in subterfuge and sabotage, which is really cool. And I can see the appeal of a class of people who left so little evidence of their true actions behind that it allowed those myths to grow.
But Pirates for life.
