None of them. Granted there is a distinction, but let's assume for the moment we've established that the sexual acts themselves cause no lasting damage. Where, then, does the damage come from? I think a large part of the damage from being exposed comes from the stigma attached to it. In which case I think it can be argued that the evil was committed not by the pornography, but by the people who have viewed and judged it.

As Elaine once said in an episode of Seinfeld (The Pick)

Because it is not me that is exposed but you. For I have seen the nipple on your soul!