How is taking what other people produced without their permission "expanding culture"?
What are the pirates *producing*?
And you're correct, though, "pirates" is the wrong term. Real pirates risked their lives for their booty. They at least had some courage. They looked their enemies in the eye and fought them face to face. Modern pirates risk nothing. I think a better term is "parasite". They live off the efforts of creative people and those who support creative people. Everytime a pirate downloads a book, *I* am being robbed. Why? Because I pay for books, and that pays not only for the book I buy, but for FUTURE books -- I am paying to help produce the NEXT thing the parasites steal.
What are they doing for me, in return?
Nothing.
Hence, parasite. A lifeform which drains the resources of another and cannot exist without its host. (No one pays for books==nothing for the parasite to steal.)