Pointless poetry exercise #4

A question that worries me: is it possible to write good poetry about a nasty person committing a nasty act? Even if it is technically possible, is it morally permissible to write such a poem? I've always said that the poet has a responsibility to write about any subject they see fit, and from any perspective - as long as the poetry's good. But now I've actually done it I feel, well, dirty and vulnerable.

"Shut up, shut up. There's nobody here!"
But I can see you, your eyes pinched hard
behind your wicker-woven fingers, your smile
stretched tight so it twangs across your skull.
Why do you hunch behind those long limbs,
my easel? You've hinged yourself into a nook
and I've dabbed my knuckles in fresh blue ink
to scribe my billet-doux across your spine -
shut up, shut up, there's nobody here
to hear you howl as I sign my name!