PayPal, probably the best known method of paying for things on the Internet has often made arbitrary decisions about what may be paid for using their services. In the past, PayPal usually banned those selling illegal goods or services, but now they seem to have taken it upon themselves to try to legislate their own morality on the rest of the world.
Chances are very good that this action is the result of one person in their bureaucracy making an arbitrary decision based on their own conclusions about what is and is not pornographic. Unfortunately, with PayPal is is very difficult to actually get to talk to a real, live person. They hide their telephone numbers very well, and rely on computer generated auto-responses to most email messages.