And, to be more exact, what kind of harm you're talking about?

I could think of some very real and large issues that are usually linked with pornography (human abduction, treating [usually] females as sexual objects, etc), but after some thinking (not very deep, I must admit) I've concluded none of them are caused by pornography itself (in a same way knives aren't the cause of homicides, although many people died stabbed with a knife). But I may be missing something.