You see the problem is everyone has different ideas of what is nudity and what is pornography and that's why places like Rendo and 3DC and DAZ have the rules they have.
If sharecg is going to sell advertising space then they may well have to react to what the advertisers expect as well. I don't know what that may well be. but I am just saying that I think a site like this has to be aware that it might be sensible not to have nude thumbnails.