Luciano Pavarotti comes to Philadelphia offering to help start a singing competition. So far, though, no one’s taken him up on the offer. “Young singers don’t need glaring spotlights. They need greenhouses to keep them incubating until they are sturdy enough vocally to survive the international-opera treadmill, with the bad airplane air, unsympathetic conductors, and high-concept stage directors that go with it. Competitions are more suited to instrumentalists. They aren’t nearly as vulnerable to the kind of permanent damage an overused voice can suffer.”