Potter was actually referring to obscenity, not pornography. They aren't the same thing. Pornography is sexually suggestive material intended for sexual arousal. Obscenity is something that strongly offends the prevalent morality at the time. (Definitions paraphrased from Wikipedia). Something can be pornographic without being obscene, and vice versa. That is, "pornography" is a description; "obscenity" is a value judgment.