Racing pigeons live a much better life than any of these "rescue" pigeons.
I don't really think its an issue unless it impedes with the birds natural functions such as eating/drinking. The majority of people who keep these breeds do anything they can for their birds health, so I don't think it is cruel.Also, what are your thought on breeding breeds like Pouters/Croppers with especially large globes, Owls with short beaks, or fantails that hold their heads so far back? Is it ethical to breed for characteristics that make life more difficult for them?