Much friction is caused by someone asking a question and others swarming in accusing him of asking a question which has already been asked.
But why not make asking such questions a legitimate act? It is not difficult to add a new tag reading something like [possibly_a_duplicate] so the user can safely ask his question.
Those who are allergic to duplicate questions then can add the tag to their ignore list and voila! They will not see nasty dupes any more.
Those who are especially keen to help newbies can add the tag to their favorites and hunt them.
I think the "philosophy" of banning duplicate questions results from subscribing to a static view of the world. One where everything is allowed to take place only once and questions are "duplicates" because the world is a still picture in which the original question is already there. Come on!
Is that how the real world looks? Should infants stop tottering because some others have already tottered?