Basically, mainstream media reflects mainstream ideas, as seen through the filter of the economic class who can afford to put it on film or TV. You don't get a lot of ideological diversity because the producers of these films/TV shows are trying to make money by attracting the highest paying sponsors -- which is determined by a show's ratings, which are generated by appealing to the largest number of viewers, i.e., the lowest common denominator.

But you already knew that.
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