In the US, what I 've just found there is a protection for the “artistic expression,” by the First Amendment, which also include internet pornography. Some call it 'social harm” ( like: http://www.thepublicdiscourse.com/2013/10/10998/), the others do not see anything wrong with it ( like: backpage).
When we go to their website, and choosing NE-Omaha: we have adults section, with the rubrics