The “Pro chickens People” are unwilling to admit that most of the chickens are simply thrown out after they are slaughtered.
They are also unwilling to admit that the feces of the chicken are a sanitary issue, that is why its illegal to slaughter animals in NYC and even to own farm animals because of the waste. The blood that comes out after its slaughtered is also a sanitary issue (However when I see Kapparot with Shechta I did not see any blood) but I did see the feces which is an issue.
If you are so gung ho on doing this, go to a slaughter house somewhere outside the city. It might be a Minhag Yisroel to do so, but there is no right to slaughter a chicken in the middle of Borough Park. The Slaughter house has proper facilities to handle the waste and will make sure the chickens go to the proper use. (There are some Muslim Slaughter houses in the city, but those are permannt places that will handle the waste, If either Kapporots could be done at those locations by renting them for a week or so or someone opens their own kosher slaughterhouse in NYC that would solve these problems)