Jonathan Swift’s satirical essay can be interpreted in two ways. One is to take at face value the “modest proposal” which the writer makes. The other is to look beneath the idea of that writer, who is a persona that Swift adopts, and consider the actual thesis to be the polar opposite of what is proposed.
In the “author’s” proposal, there is an underlying, combined premise: that overpopulation exists, and that it is a serious social problem. This author does not look beyond that obvious problem to consider what type of people there are supposedly too many of, but assumes that overpopulation applies to the poor. His solution to this problem is to reduce the number of people quite early in their lives: that is, as infants. There is a certain, irrefutable logic here, because if the babies are not allowed to grow up, they will not consume scarce, valuable resources. At base, the proposal is to eat the babies.
In contrast, if we deconstruct the essay from its basic assumptions onward, we can see how Swift is poking holes in the underlying arguments that are so often put forward. He basically rejects the premise that there are too many people, especially poor people. Rather than eat babies, society should nurture them and provide resources for them—and their parents.