In addition to the higher frequency of both fraud and chargebacks associated (allegedly) with sexual content, there are also a legal concerns for payment processors. They don’t want to be associated with enabling child porn both from a legal responsibility angle and also from the perception of processing payments for illegal content.

Is that concern overblown? Probably, but the card companies do get pressure from both the public and the government when they process the ‘wrong’ teansactions whether they are illegal or not and they don’t have a free pass like the internet common carriers do.