Batman is all things to all people, where "all people" can mean both the citizens of Gotham City and generations of comic fans. Christopher Nolan's films made Batman a serious subject for an even wider audience, and reviewers and commentators have read into them all manner of political messages—messages which typically say as much about the analysts as they do about the films.
For my part, I could go on for a while, telling you what I infer from the Animated Series Bruce Wayne's attending so many environmental benefit galas versus the Dark Knight Returns Batman's relationship to Ronald Reagan. But, like pundits rubbing their chins as Nolan's Batman and Bane grunt at each other, I'm sure to see exactly what I want to see.
For example: The fact that Batman refuses to kill anybody would seem to imply unambiguously, to some, that he is anti-death penalty. But any fan who wants to say he's pro-death penalty could form an explanation: "He's sworn to do what Gotham's police cannot, and while tracking down, walloping, and apprehending criminals are all powers he grants himself, he leaves the handing-down of death sentences to the judges." The arguments both come down to speculation, and the worst part is that either reading, or both, or neither, might be correct, since the truth of who Batman is in a given story is in the hands of that story's author.
Have any of Batman's writers, in any medium, made him voice a specific political belief, or confirmed outside of their work that "my Batman believes such-and-such"?
I am not looking for inferences—again, this is a situation in which anyone can infer anything. The exception to this would be an inference drawn from overwhelming and overt evidence sourced from a single author, such as a story arc where Bruce Wayne is conspicuously absent from a series of board meetings that coincide with the dates and times of Nader rallies.