Opera for stupid people - a slogan for stupid people. This kind of epithet has been aimed at Puccini and the "verismo" opera form in which he excelled.
Musical theatre - at its best - is worthy of standing at the side of opera as a serious, meaningful art form.
Oscar Hammerstein believed that much of what passed for entertainment on the stage was worthless. He had worked with Jerome Kern and Rudolph Friml and knew that it was possible to produce meaningful and serious musical theatre. He was associated with the Theatre Guild (a kind of middle-class co-operative concerned with raising standards in popular entertainment) when Richard Rodgers (whom he had known practically all his life) became available due to the death of his long-term lyricist Lorenz Hart. Rodgers was a product of the institution now known as the Julliard School of Music.
Theatre Guild wanted to produce a musical version of a play whose rights they owned called Green grow The Lilacs . The result, renamed Oklahoma! was the first "book musical" in which music, song and dance are all used to advance a plot and tell a story. Oklahoma! actually includes a reference to the sort of musical entertainment which Hammerstein despised in the song Kansas City.
Hammerstein's surrogate son, Stephen Sondheim, wrote the lyrics for West Side Story.