Could somebody please explain the Poem 'Pink Dog' by Elizabeth Bishop and the prejudice expressed in this poem?

This poem refers to a historical event in 1962 when beggars on the streets of Rio de Jainero were being cruelly murdered by the "Death Squad." In this poem, the speaker is started by the sight of a "pink dog" who is completely hairless and clearly suffering. This leads her to meditate upon what is being done to other human beggars and the kind of fate that such a pink dog could expect in such an environment. Consider how the speaker asks the dog if it knows about the kind of fate it can anticipate:

Didn't you know? It's been in all the papers,
to solve this problem, how they deal with beggars?
They take and throw them in the tidal rivers.

The slaughter of innocent people who are unable to defend themselves is thus explored with notes of sarcasm and black humour in this poem. This has become such a common occurrence that, we are told, "all the beggars / Who can afford them wear life preservers." The prejudice that this poem directly addresses therefore is that beggars and the down-and-outs of society have nothing to contribute to life and are better of being executed.