The ways of poetry and music are not changed anywhere without change in the most important laws of the city. So wrote Plato in the Republic (4.424c). Music, for Plato, was not a neutral amusement. It could express and encourage virtuenobility, dignity, temperance, chastity. But it could also express and encourage vicesensuality, belligerence, indiscipline.
If I had a teenage child with a passion for serious music, I would not hesitate to give him or her "Essays in Musical Analysis" by Donald Francis Tovey.