English National Opera is producing “On the Town.” “There is more to opera than Mozart and Wagner, and if Johann Strauss could upgrade from music hall to opera house then why not Oscar Hammerstein? La Scala, after all, is preparing to stage Lloyd Webber’s Phantom and, as for preserving the purity of the naked voice, it is an open secret that New York’s high-church Met has, on occasion, amplified a mezzo or two. Covent Garden took on Sondheim and the National Theatre has made Cole Porter core repertoire without anyone questioning their core purpose. Why, then, is ENO under fire when all it wants to do is reach a wider audience?” Well…