Kaufman, I would hope, uses him simply as an example. Even the worst types of people deserve a voice. We see, ultimately, the embrace of the Marquis' writings by the institutions, when it becomes evident that a profit can be made from them. Anything for a profit. And finally, the simple message, that trying to stamp out those undesirable elements only makes things worse.
Movies are always a hot topic in terms of censorship.
As well he should. Quills is disturbing because of the perspective it takes. There are so many things in the film that, if they were in any random movie, most people wouldn't think twice about. Violence mostly, and sex to a lesser degree, are in movies all the time. But when confronted by them in a movie that is basically about being confronted by them, the effect is different.