Not sure where you get that for pornography, a large number of studies and projects have been done - especially since the late 1940's. Except those done by people with an ax to grind on to chop it up and burn it, the evidence is heavily for it being mostly harmless except for persons who have deficiencies in certain types of mental function where sex is a consideration. There is a lot more to this and I have too many other interests to go on and on with this.......
Note, my specialty is the type and scope of the porn over time. Many things go in and out of favor - mostly a cycling of things of most interest to the general public.
Couple of fun points here though: Japan and Germany are both countries with cleanliness concerns that are well ingrained yet a reasonably large percent of their porn material (app. 25-35%) involves waste material. Countries such as France, Germany and Italy go big for priest and nun (with or without civilians as it were) or preachers (not Catholic). The US, of course, is big on most everything so can't be specific for it. There is more but I suspect forum management would not be happy if I clarified.
On the bright side, it is correct though.