When the Boston Symphony hired James Levine as music director, it knew that its audiences would be in for a healthy dose of modern music amid the Sibelius and Beethoven. But less than a year into Levine’s tenure, some are beginning to ask why the maestro seems to go out of his way to select the most tiresome, unlistenable examples of 20th and 21st-century music. “Most of those contemporary composers favored by Levine, such as Elliott Carter and Milton Babbitt, have little patience with anything that smacks of tonality or emotional catharsis. These sons of Schoenberg… also could not care less about music that could rebuild an audience for classical music.”