Of course you have to pay if you go to see it in a movie theater, or you to to a concert -- its their building after all! And I for one am glad to pay for that; after all, I don't have a big screen TV or surround sound. Plus, leaked copies of movies tend to be of poor quality.
Other than that it shouldn't be mandatory. I am a strong believer in voluntary donations. If people think something is worthwhile they will support it if need be, either financially or through some other means (programming, donating equipment, advocacy, etc.) otherwise it will just go away, but if nobody cared enough to support it is it really such a big loss?