Studios putting out blockbusters do not want their movies to be tied to any sort of political sides because it would mean less money for them. And with blockbusters, they are trying to make as much money as possible. In this quick answer, Chris Nolan responds to a question and makes it clear that his Batman movies are not intended to be political:
On a side note, Rachel Maddow discusses Rush Limbaugh's Bane Conspiracy Theory:
I would also like to add that, in my opinion, any liberal artist would not create a work supporting conservative ideas. From the contribution records of the Nolans and Goyer it is clear that they are the typical movie industry liberals - whether they are moderate liberals or complete socialists is something they only know. And it surprises me that the word socialism is still used as a dirty word by the conservatives. I think both sides, the left and the right, have good ideas - it is a matter of working together rather than trying to find differences in ideologies for selfish egomaniacal reasons. Again, that's just my opinion.