The emotional energy of Sylvia Plath's "Daddy" comes from her allusions to Nazis and the Holocaust to illustrate her own experience, feelings, and suffering. It is a raw, powerful poem--one of the best I've ever read.
Still, I can see something distasteful in using the industrial slaughter of 6,000,000 Jews to illustrate one's poor attitude toward one's father.
Alfred Hayes' "The Slaughter-House" begins with a description of animals suffering in a slaughterhouse. In the second half of the poem, however, the animal hanging upside down on its way to be butchered becomes a symbol for the poet's "private woe."
Again, I see something distasteful here: is Hayes' suffering, whether in a relationship or general existential suffering, comparable to a living creature hung upside down on its way to be slaughtered?
But then, poets look about their own worlds to illustrate their own feelings and ideas through poetry. Plath wrote "Daddy" shortly after Eichmann's trial. Hayes may have been at a slaughterhouse and felt it described his own sufferings. Poets find the image necessary to convey the idea--and it doesn't matter who finds it objectionable. That's poetry.