I should say that the question of whether the poet is using his poetry to advocate or attack a social attitude does not matter. Bad verse may have a transient vogue when the poet is reflecting a popular attitude of the moment; but real poetry survives not only a change of popular opinion but the complete extinction of interest in the issues with which the poet was passionately concerned.
Lucretius' poem remains a great poem, though his notions of physics and astronomy are discredited; Dryden's, though the political quarrels of the seventeenth century no longer concern us; just as a great poem of the past may still give great pleasure, though its subject-matter is one which we should now treat in prose."
"The Social Function of Poetry" in On Poetry and Poets by T.S. Eliot