By downloading a film, even if you don't pay for it, you are contributing capital to that film. You'll cache the the plot, characters, actors in your mind and likely talk about it with your friends & collegues --in social situations re-enforce the film's value and reify the investment others have made by paying for the film.

If you don't see the film, and one of your friends has a film reference you don't recognize, you're actively not helping the film monopoly since the time your friend invested in the film has no value to you. In this way, you're denying the network effect.

The films don't need everyone to pay for it, only a fraction. By pirating a film, you contribute the most important thing you have: your mind and social attention.