"Many of those who condemn "porn" seem also to believe that sex is bad as such, unless redeemed by some approved thing"

Good point. Like you say, there is some kind of formal sanction for 'erotica' that thereby elevates the material 'beyond' the sexual realm, and thus makes it safe to indulge in without worry that you are somehow debasing yourself.

There's something Sooo self-deceptively 'Brave New World' about that. One of the most amusing examples would be archeological or anthropological porn, which one may admire at an intellectual distance for it's possible historical/cultural interest but *never* for it's universally applicable immediate sexual reality.