I think the only truly effective way to teach morals (because "teaching morals through lyrics" is essentially what is proposed here) is through experience. Basing (or simply adjusting) your behaviour because of what someone else wrote doesn't ensure that you'll internalize the reason behind the message. Learning from lyrics is no different from basing your behaviour upon what the Bible says, or what your parents say. If the message is going to have a real effect on you, you must be aware of the message's implications.
Jeremy tells the story of a kid who had a bad home, was picked on in school, and committed suicide. You shouldn't take away the lesson "don't pick on kids or they might end up committing suicide" because that really goes no further than establishing a tenuous cause-effect relationship. Do we need another song saying "don't pick on kids or they might shoot up a school"? I don't think so. People need to empathize with others to understand the effect of their own actions, that way building sets of rules (via songs, the Bible, etc) is unneeded. What happens if a rule hasn't been established yet? Well, I guess there's a good chance you'll fuck up... unless you can stop and think "how will this action effect this person?"
i could probably structure this arguement better, but i'm lazy
basically, you haven't learned anything by adding another entry in your book of "things to not do" because that allows the excuse of "i didn't know that thing was bad - it wasn't in my book". hmmm, maybe i could use set theory here... nah, that would be too dorky even for me