Most of our rules have evolved over time due to certain situations arising. So for example...
4. FAMOUS MALE NUDE IMAGES
Full frontal nudity is not permitted if taken from:
Any 'home video' or images distributed via the net or other means showing famous males engaging in private sexual activity or stills or images from such a video. Including mobile phone video and images.
This rule was needed as we had legal threats to remove several sets of nude images taken on a mobile phone. They were personal to the celebrity and were classed as private. We weren't the only site forced to remove such pictures. So now, as a precaution, we have a blanket ban on naked celeb self pics taken using a mobile/cell phone. This protects the privacy of the celbs when the pics weren't intended to be made public, and protects us from lawsuits.
The non-porn rule arises from the fact this is not classed as a porn site, but a site where pictures that are in the public domain already can be shared. Given the ethos of the site is Famous Males, we don't class porn actors as famous, as they are only known within the porn industry, and generally don't appear in glossy mags in WHSmiths etc.
The over 16s only rule came about recently as sexually gratifying remarks about under 16s were being made. If members want to enjoy semi-clad images of minors, they can go somewhere else, as allowing that here would start pushing us in a worrying direction.