You say that we exclude significant material on the basis of notability? That seems almost contradictory. If it has been the subject of non-trivial, reliable, 3rd party coverage, it's notable. If it hasn't, how 'significant' is it really?
As for childish, trivial, offensive stuff: is it an encyclopedic topic and notable? If so, it's hardly trivial. If not, it should go. If we chuck out everything which offends some significant group, we lose NPOV and balanced coverage. That doesn't mean I don't believe we have non-notable offensive articles, just that we should use our policies effectively to get rid of them.