Clearly this part of this hilarious and grimly satirical essay is part of Swift's design of creating a speaker who is above all trying to present himself as reasonable and logical in the way that he proposes a horrendous idea. If you read through the six advantages to turning Irish children into a form of human cattle for consumption, one is struck by the emphasis on reason and logic in the arguments that the speaker uses. All would benefit from adopting this measure, from the English landlords to the poor themselves, according to the chain of argument.
Of course, such emphasis on an appearance of logic and reason only serves to augment the true horror and disgust that Swift is trying to produce. In reality, the poor would suffer even more than they were during the famine in the first place. Thus it is that Swift shows how adopting such a logical, reasonable and statistical view of humanity can result in converting ourselves into monsters whilst also protesting against the inaction of the English in doing nothing to alleviate the horrendous conditions of the Irish famine.