Nicholas Knight said:
No one, NO ONE, has said any sort of filtering must take place by default.
All these arguments about appeasing those who will attack us for not filtering, are meaningless if a non-logged-in user approaching the site for the first time will see the images that it is proposed should be filtered on the grounds that most people may be upset to see them. So what's the point of filtering if we only do it for people who are motivated enough to either create a user and log in, or fill in a form saying what kinds of image they want to have filtered?