Some sensitivity is certainly in order, but unfortunately a lot of the world's great music has been co-opted in support of pretty awful things. The Nazis provide one of the biggest examples of this -- their movement had a built-in soundtrack, everything from "Deutschland Uber Alles" (a profoundly beautiful tune by Haydn, I believe) to the music of Bach, Mozart, Beethoven and Wagner. Of course, most of this doesn't contain objectionable lyrics, which can be hard to ignore sometimes. I'd say preserve it all (you preservationists out there), but consider your audience before you sing something too insulting.