BigAl, I agree that art rarely performs miracles, and need not always be directly do-gooding. But we have the right, and sometimes the obligation, to comment on moral and other issues in works of art.

Poetry and music do have the potential of igniting revolutions; think of La Muette der Portici". The effect in any special case cannot possibly be predicted and rarely proven from hindsight, but is generally hard to deny. And yes, I am sure some songs did increase or decrease the number of people murdered, even if it can never be measured.

Apart from the literal meaning of poetry, the tone can make a difference. The subtle art of ranting is to convey justified outrage rather than joy of quarreling.