Movies that are exhibited in theaters have a rating given by the MPAA: G, PG, PG-13, R, or NC-17.  Your rating determines how many screens will show the movie, and therefore how many people will see it.  It even affects, to a lesser extent, DVD distribution, as some DVD rental outlets don't carry NC-17 movies.  The point of "This Film is Not Yet Rated" is that the ratings system has the effect of favoring big studio movies over independent films, and that this is counter to free competition in the marketplace.  Other specific areas of bias are gay/lesbian sex versus straight sex; the former...