The screenplay talks a lot about American democracy, the Constitution, and Thomas Jefferson, but it also speaks about happy peasants, class warfare, and the evils of fascism (instead of totalitarianism, which would encompass all "isms")
So is BORN YESTERDAY really about American democracy, or something else?
I think it's really about Billie growing up and realizing that she doesn't have to take crap off of her boyfriend anymore. That she deserves something better. When she reads that famous Thomas Jefferson quotation: I have sworn eternal hostility against every form of tyranny over the mind of man, I don't think the movie is trying to make a political statement at that point. She reads it and thinks, "Gee, I shouldn't let myself be oppressed anymore; I'm sick of not thinking for myself and not living my own life."
So, to answer your question concisely, I really don't think this movie is about American democracy at all- women's liberation, perhaps, but mostly, I think it's just good fun.
I felt that the message being conveyed was to be your own individual. By the end of 'Born Yesterday' Billie manages to be independent in her thoughts and actions rather than being controlled by Harry as she had been before her transformation.
"I'd rather be hated for who I am, than loved for who I am not".
What ladylavende and Errington_92 said. It's really a feminist film about a woman discovering her own identity and power, then getting out of an abusive and controlling relationship.
There is also an anti-classist message in that Billie's a lot smarter and stronger than people assume she is based on her voice and untutored mannerisms. Once she becomes educated, her mind is opened up to different viewpoint and possibilities, not just a new "right" way to see things.