Although one of those present said, that "one must be raised with that kind of music" in order to appreciate it, in reality I was not raised with Wagner, nor with opera, nor with serious vocal music at all. One must cultivate one's ability to enjoy various arts, and especially the incredible variety of music over the centuries and across cultures. In my home, I heard popular music and jazz more than anything else, but some "classical music" on occasion. My father loved Beethoven, Tchaikovsky, and especially Gershwin, American jazz, and big band music--all of which I can appreciate to this day. My mother liked pop music on the radio, and country western (which my father hated and mocked); but my mother's special love was for the "golden oldies" from the 1920's through the 1950's or so. My father's father, a truck driver, loved opera, and especially Italian opera, and I remember at least once seeing him sit by the radio listening to opera, although the memory may be reconstructed from what my father told me about his father. The strongest influence on my appreciation of serious music came from my sister. She took piano lessons, and would often play sonatas by Beethoven, music by Bach, and so on.
One incident stands out as highly formative in my ability to appreciate serious music: One day, when I was five years old (living in Rochester, New York), my sister had me lie down on the sofa when I came home from school, and she played for me a recording of Grieg's famous "In the hall of the mountain king" from his "Peer Gynt Suite." She told me the story briefly, and I could picture being chased down the mountain by an ogre. What a gift she gave me at that moment. That really began my love of serious music.
But all loves take work and cultivation, and over the years I have spent much effort teaching myself to appreciate good music. Sometimes I study scores, or at least follow them as I listen to music. But often, I simply listen to a composition, and try to think about what I am hearing, and observe what effects the music has on my soul (mind, feelings). Self-education in one's ability to appreciate beauty is crucial in life. Simply to put the mind in neutral, and listen passively, is lazy, and deprives one of the joy of discovery what the composer was doing in the music, and how the artists are interpreting it and communicating it to listeners. Again, to learn to appreciate any art takes much effort and study, although initial sparks can come spontaneously. This experience fully parallels human love: there can be an initial spark of "falling in love," but real love takes much work, many choices, and "dying to self" in various ways. So it is with enjoying and appreciating music, poetry, painting, photography, philosophy. To live well takes much work. Why should the appreciation of music be different? It is not.
Now, regarding the case of Wagner's "Liebestod" ("Love-death") that concludes Tristan und Isolde: I know well the problems with Wagner, not only from reading Nietzsche's analysis, but from listening and observing the effects on the soul. Wagner's ability to move the passions is amazing, and must have been the main reason Hitler so loved Wagner's music dramas, and tried writing an opera in Wagner's style. The Nazi sense of drama on a grand scale owed much to Wagner, and we know that Wagner's heirs and the Nazis formed some very close ties, but I really doubt that Wagner would have been a Nazi. (Nietzsche would have hated the Nazi movement as a most degenerate form of herd mentality, although the National Socialists made much use of bowdlerized passages from Nietzsche's writings.) But there is a similarity between Wagner and Hitler which has been widely observed: Manipulation of the masses was the common thrust. The way that Hitler could move masses in his hysterical and histrionic rants had been anticipated in the moving of masses through music, and perhaps most notably through the intoxication and delirium effected at the Wagnerian Bayreuth festivals.
In the generation before Wagner, of course, there was Beethoven, who clearly unleashed a new era in the musical manipulation of passions in his highly revolutionary Eroica Symphony (1803)--the composition that must be the single most influential work in the history of modern western music. From its opening crashing chords, Beethoven brilliantly and most effectively communicates his rage at existence through orchestral sound. Although the Eroica is magnificently composed, and much "rock music" is dashed off mindless sound, these musical works have in common the immediate expression of feelings, and especially of intense anger. (For his part, Wagner's soul is much less driven by rage than was Beethoven's, but both exemplify Nietzsche's analysis of "die Wille zur Macht," "the will to power.") One can go further back to Luther's hymns, such as "Ein feste Burg ist unser Gott," ("A mighty fortress is out God"), to observe music as propaganda for a modern mass movement. The composer seeks not only to express himself, but to assert his will over the minds and hearts of hearers. This will to power is clearly evident in the examples noted, but grows in intensity and effectiveness over time, from Luther's hymns, to some of Beethoven's symphonies, to Wagner's music dramas, up to the Nazi movement. As an example of Nazi art as will to power, and as a spiritual successor to Beethoven-Wagner, see the brilliant and artistic masterpiece by Leni Riefenstahl, "The Triumph of the Will." The viewer is moved to feel awe and even "reverence" at the Nazi heroes and "ideals" displayed on the screen. This is effective (and damaging) propaganda.
There may be truth in the claim all art can have an element of manipulation in it. But surely not all art is destructive or malformative of the human soul. What matters is not only the purpose of the art, but whether it instills restraint and self-control, or wild abandonment, in the human psyche. This claim needs further exploration and proof, but let it suffice for the present to note that Wagner, for one, intoxicated his hearers-viewers. While I can readily appreciate Wagner's skill in manipulating his audience, much of it is, at the same time, degenerate art, as Nietzsche came to understand. One can allow oneself a little Wagner, without being corrupted. Or a little rock music, without being corrupted. But much exposure to highly manipulative art corrupts the soul badly, whether the music be that of Wagner, or much of rock music. This ought to be clear to anyone who understands music and the human soul.
Palestrina, Tallis, Bach, Haydn, Mozart, for examples, elevate and refresh, with minimal corruption. Listening to true spiritual masterpieces in music can indeed elevate, ennoble the soul, and even give its glimpses of "the Beyond," of union with the One manifested in the many. Again, this issue needs much further exploration, but let the bald statement suffice for the present. This much is clear, and needs to be understood by parents and educators: Healthy souls create healthy music; sick souks create sick music, and spread their disease. The disorder of rock is very harmful to children--often, it is poison. And yet the hearers do not know it, and parents wonder why their children seem to become unruly, at worst, young criminals in the making. Degenerate music contributes, by breaking down order in the soul, and instilling lawlessness, disharmony, and sheer immersion in destructive, excessively passionate forces in the soul. By contrast, Tallis, or Bach, or Haydn, cultivate the sense of beauty, of balance, and surely educate the intellect in studying what is good and beautiful. And they calm and help order the soul. At their best, the truly great composers help to elevate the human soul into God through the love of the beautiful and union with the One. (Again, this truth needs much more development.)
All of this, and more, was analyzed by Plato in the Republic, written in the 4th century before Christ. Education in good music is crucial. Bad music, bad art, corrupts. Anyone with sense can understand that. Just listen and reflect on the effects in one's soul.