... One year ago, a new library designed by world-class architect William Rawn opened on Mattapan’s Blue Hill Avenue, a street rarely associated with first-class anything. [...] But the highlight of the new library was its young adult room. [...] In reality, some of the young people are throwing punches, hurling insults, and tossing furniture in the space that Rawn designed as an “oasis of safety.’’ It doesn’t happen often, but often enough to draw negative publicity and discourage some adults from patronizing the library. The good kids who easily outnumber the thugs know what comes next. “People will say...