Answer: Greedy Irish property owners exploit the helpless poor.
In "A Modest Proposal," Swift proposes to deal with the problem of poverty in Ireland by eating poor Irish children. This, he argues, will both reduce poverty, and provide rich landlords with a delicious source of food. His purpose in writing the satire is to call attention to the abuses of the poor class by the gentry. In this passage, he argues that eating the poor children is only natural for the greedy, rich class as they have already "devoured" the poor parents (by constantly exploiting and abusing them).