At a site like Megaupload (it has many copycats) someone will upload (share) a movie. You can either download it at a slower speed for free (that's where the sharing part comes in) or buy a premium membership and get it full speed with no nag screens. You aren't paying for the movie you are paying for the speed and convenience. The person who uploaded the movie is rewarded either in cash or credits that can be used to extend his premium membership based on how many people downlad his movie. He's not being paid for the movie itself he's being paid for bringing new users into the site. The owners actually don't get involved in either end, they make their money off of the premium memberships, which will probably be their defense. They do delete files for copyright infringement but 99.9% of the copyrighted material slips by their enforcers, which will be the government's case.
Even if you shut down every file sharing site there would still be multiple ways to get the movies. Heck, even Usenet newsgroups and IRC still share movies after all these years and advancements in technology.
Too much hassle.
I’ll stick with NetFlix.
;D