Symbolism, Imagery, Allegory
Were the English really cannibals? Unless we skipped a chapter in British history, it's more likely that eating is a symbol. It's a pretty important one, too: Swift felt that the Irish poor were being consumed at a rapid rate by the wealthy classes.
It's a vicious circle of life. At the age of one, kids start to get hungry for more than their mother's milk. There's no more perfect time to feed the kids to their more fortunate peers, the narrator suggests. He makes it perfectly clear:
Secondly, the poorer tenants will have something valuable of their own, which may be made liable to distress and help to pay their landlord's rent, their corn and cattle being already seized, and money a thing unknown. (21)
It seems pretty clear that the foodies aren't doing all of the eating, so to speak. The richy-riches who plough through resources and throw pennies at the poor have plenty of practice devouring the nation. Even better, most people who could read in 1729 would fall squarely in the category of the eaters. Chances are that if you picked up A Modest Proposal, the satire would be directed at you. Yep, you.