I don't see why it's illegal.

As soon as there's an active and recording video camera there it's suddenly legal, and the actors earn money from their recording.

Paying a man or a woman to provide you sexual favours is no different than treating yourself to a chocolate bar at the local shop in my eyes. It's something that's obviously going to make you happy, and why should anybody else care what (or who) you spend your money on?

Just another idiotic social law that has found itself unwritten over time in the book of other idiotic social laws.