To my understanding (I don't listen to any of these), there are positive messages in hip-hop/rap music and negative messages, positive messages in country-western music and negative messages, positive messages in death metal music and negative messages. However, you have only mentioned one of these three. I can't tell you why that is, but that's something you need to ask yourself and think about, if you want to be as enlightened as you seem to be trying to be.
As for the Cuban teenagers, it seems to me that people choose music that reflects their inner selves, rather than adjust their inner selves to their music. Whatever the situation that caused them to be refugees in the first place, it probably created a lot of anger or resentment, and they found an echo to that in their music of choice. The real question is did it interfere with their ability to function (go to school, get work, etc.)? If not, why would it be an issue at all?