What about U2?
Some rap definitely has a message.
And lest we forget...Sarah McLaughlan and "In the Arms of the Angels" which she has determined is an animal rights song....

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Poor Spot! He was tired of being thought of as stupid. "I'm gonna join Mensa," he said to myself, "and then I'll be legally permitted to wear the society's insignia--a tattoo of a little map pin pushed into my flesh--and then everyone'll know that I'm not dumb at all!"
Spot Joins Mensa
by James "Kibo" Parry