Quantification and dehumanization go hand-in-hand in "A Modest Proposal." Swift views children and even parents (who he calls "breeders") solely in terms of a cost/benefit analysis. He calculates, for example, how much it costs to nurse a child "just dropt from its dam" in its first year of life, and suggests that his scheme represents a way to make these children, which he deems a burden on Irish society, "contribute to the feeding, and partly to the cloathing" of thousands of people. His "proposal," of course, is to take hundreds of thousands of Irish children and use them for food. A "good fat child," he assures the reader, will fetch a price of at least ten shillings, turning these "burdens" into sources of wealth.
So Swift (satirically, it must be remembered) dehumanizes the Irish by referring to them in exclusively economic terms. Indeed, this is part of the power of the essay, and, in a word, Swift's point. He wants to show the reader that enlightened, coldly rational schemes, while well-meaning, need to keep the humanity of man in mind. When we think of people solely as statistics, we lose sight of them as human beings, a point Swift makes clear by carrying the commodification of human beings to an absurd conclusion. So, in short, Swift dehumanizes the Irish through quantification.