I was reflecting on the morality of music while I vacillated over what genre of music I should listen to; I was thinking either in-your-face-punk metal or soothing country.
I felt like getting mad so I was naturally tempted to listen to the metal. But I knew that getting mad would not be good for me at the moment, so I finally decided to go for the country.
It was at this moment that I finally realized what was the key aspect that determined the morality, or immorality, of music. It seems that music is in itself an amoral dynamic, but it nonetheless influences the thoughts, feelings, and even actions of the individual listening to it. So the answer seems to be that of edification, how does the music affect the listener? But because the morality of a certain piece of music cannot be objectively measured since it is dependent upon the listener, it is an entirely subjective matter, because what might influence one person positively might influence another negatively. What follows then, is that the music which edifies is good, and the music that negatively influences is wrong.
But I am afraid this is a tragic oversimplification. It was one of Bach's most cherished convictions that every type of music, even secular, gives glory to God, because it is a way that the musician expresses the talents that God has given him.
I do not pretend to have all the answers, and my conjectures are tentative and liable to any sort of correction. But I am most certain that music, of almost every type, can have a positive impact on your mental health. It seems to be one of the two known universal languages, mathematics being the other.