I think that both Mill and Sidgwick are great and admirable philosophers, from whom we still have a lot to learn. I would not favor a form of Kantianism (if there is such a form) that treats Mill's or Sidgwick's moral philosophy with disrespect.
My theory is that poems are written because of a state of emotional irritation. It may be present for some time before the poet is conscious of what is tormenting him. The emotional irritation springs, probably, from subconscious combinations of partly forgotten thoughts and feelings. Coming together, like electrical currents in a thunder storm, they produce a poem. . . . the poem is written to free the poet from an emotional burden.