Swift knows that there's something rotten in the state of Ireland, and it's not the food. Nope. In A Modest Proposal, Swift is calling out the fat-cat landlords who stuff themselves silly as their tenants starve to death in the streets. Here's the problem: those same wealthy jerks were also the ones reading Swift's work. After all, the poor people were too busy figuring out how to survive to learn the alphabet. So Swift includes plenty of examples of suffering to clue his readers in to exactly what's going down in Ireland.
Swift tries to spur rich readers to action by providing both sickening examples of suffering and a ludicrous solution, since he knows that facts alone are ineffective.
A common line of thought in Swift's day said that a country's riches were its people. By the end of A Modest Proposal, the narrator seems to suggest the opposite: the only way the Irish can contribute to their country is by dying.