When your competing movie has all kinds of bells and whistles, shots of real helicopters and aircraft carriers and all -- and you can't afford to have that because you don't have access to the stuff that the competing movie got for free, this puts you at a disadvantaged position at the box office. Movie production is pretty damn expensive: these days it's not at all surprising to see film production budgets exceed hundreds of millions of dollar (the last Pirate of the Caribbean cost $300 million to make). When movie studios are under the kind of financial pressure that they usually are -- leaving aside advertisement costs, this can actually be a make or break point for them. So, the government is incentivizing the production of a certain kind of movies... and we see the effects of that play out.
A recent Pew research piece revealed that 7% of Americans use Reddit, and the significant majority of that 7% is millennials. If you go to Reddit you probably know they overwhelmingly support Wikileaks (and/or Assange), so the argument that there's no demand for content that challenges America is very weak (whether it be related to the Wikileaks scandal or not). If a high production value movie unabashedly cast Assange as a hero without faults, the movie would be accepted fine by a sizable amount of people, it would make a lot of money: a lot of people see Assange as a mystical hero, they'd shell out money to see that movie.