The purpose of Swift in using that type of language is to imply that the English think of the Irish as inferior beings, comparable to livestock. The words breeder, carcasses and flesh resemble those used by butchers when talking about cows.
The use of statistical data develops this idea by placing practicality as the main factor in determining the Irish people's destiny. It reinforces the idea of them not being any better than livestock in the minds of most rich English people.
