In November, in an effort to ruin my life, my sister Rachel disagreed with me about Bob Dylan (whose composition efforts I enjoy, but whose performance efforts I abhor). This of course occurred right when I was leaving for a big conference and was too busy to reply. But in the meantime, I've thought a lot about it and decided to formulate a better explanation of what I dislike and why.
Music serves different purposes for different people, but to me, music is kind of an aural riddle, constrained by certain rules, that challenges my mind and influences my emotions. When it's something I like, I listen, my brain is stimulated, and I enjoy it. For example, if I'm in a good mood and I listen to a "sad" song, I enjoy the wave of sadness that contrasts with my baseline emotional level. If I'm in a bad mood, I get pleasure out of commiserating with a collection of sounds that are feeling the same way I am.
When I say rules, I'm thinking of the rules of music theory and musical traditions and conventions. This is of course quite fluid over the course of history, and probably one of the reasons I loathe Baroque music quite as much as I do is that it's too constrained by theory rules. I enjoy Medieval and Renaissance music, however, because while it is constrained by the rules of its day, those rules are so different from modern music theory that it is interesting.
A clever composer/artist/whatever can get away with bending or even breaking certain rules, and I like it. But, there are certain things that to me are non-starters. Bad intonation is one of those things. It distracts from the riddle. All I can think about is how off it sounds. And this is what I dislike so much about Bob Dylan.
There is music from other cultures that contains notes that one could not play on a piano -- quarter tones, which fall between adjacent keys on the keyboard. In the context of that cultural musical tradition, these "off-key" notes do not bother me in the least -- it's part of the setting of the riddle. But when we have a Western artist who is clearly playing by Western rules and then singing notes that do not exist in the context of Western music theory,* this is a dealbreaker for me. I don't perceive it as Bob Dylan bending or breaking the rules of Western music theory -- if he were, I would expect to hear the accompanying instruments also coming out with quarter tones. No, Bob Dylan is just being sloppy, and I don't like it.
* There are cases when quarter tones are used in Western music for emotional effect, such as in Jerry Goldsmith's soundtrack for Alien. He's using these "alien" notes to create a disturbing musical background for a disturbing movie foreground. This rule-breaking works in this context. Again, I don't think Dylan is deliberately using quarter tones to create a disconcerting aural environment -- that goes against the context of the words and the rest of the melody that he's singing.