Yes, pornography is protected by free speech. There are many famous cases in which the judicial system has ruled in favor of the publishers of pornographic material that state that pornography is protected by the constitution. One such example is the case of Larry Flint the publisher of Penthouse magazine who won his free speech case in the US Supreme Court.
I believe that in some cases pornography is a way that some people can express themselves artistically and that by that fact it is protected by free speech. I also believe that porn is a way for people to for people to rebel against society and learn to find themselves. There is really no difference between porn and low budget films.