In practice it is protected, but as the law is written it's hard to say how or why. Pure pornography with penetrative sex, by any reasonable definition, "depicts or describes, in a patently offensive way, sexual conduct" and "lacks serious literary, artistic, political, or scientific value". And it's pretty clear that most pornography is intended to "appeal to the prurient interest". So it's really only protected because juries refuse to convict, meaning it's only protected if the defendant is seen as likable.