For some people porn can be very "dangerous", people with addictive personalities for example.
Of course one can say that about Sports, smoking, drinking, gambling, etc. pretty much anything that can be addictive.
I know couples that enjoy porn together for example, not to "start the engine" sort of speaking but because they enjoy the "semi-voyerestic" aspect of it.
As Christ said, it is not what goes IN a person but what comes OUT, the poisons them.
That said, there are some people that are effected adversily by porn, that view sex as "porn" as opposed to "love making", that view women as "hump toys" as opposed to loving equal partners.
Of course those people and their type have ALWAYS been around, even before mainstream porn, and have always "acted out" those views anyways.