Part of the immense humour of this passage is the tone that the speaker uses to make his "modest" proposal. On a literal level the speaker's tone is earnest and straightforward. On the satirical level the tone of the essay is bitter and sarcastic. The preposterous nature of the speaker's proposal is evidence of the satiric tone of the essay. However, also key to identifying and characterising the speaker is his use of language, and how this ties in with the nature of the satire.
Note how the speaker refers to mothers as "breeders" throughout. He also recommends "dressing" the babies shortly after slaughter, as if they were roasting pigs, and urges husbands to treat their pregnant wives well - just as farmers do their mares, cows and sows.
Swift then creates a speaker who, through his earnest tone and choice of language, only serves to highlight the satire of this excellent essay and underline the plight of the Irish and the cruelty of the British in doing nothing.
Swift modeled A Modest Proposal (1729) on the many such proposals, written by writers often called projectors, designed to reform political, social, and economic problems in Great Britain, but most especially in Ireland, at that time probably the most economically exploited part of the country. Swift, Irish himself, had a long history attempting to convince the British that the economic exploitation of Ireland was against their interests and a gross violation of human rights. A Modest Proposal is still considered the best example of irony in English literature. Unfortunately, as good as it is, the irony was lost on the English.
For such a proposal to be credible, even though the proposal is horrific, inhumane, outlandish and any other negative adjective one can use, the proposer must appear to be realistic, unsentimental, economically sound, and eminently logical. He must, in essence, want to solve a problem in the most reasonable and beneficial manner possible. Swift goes to great lengths to establish the objectivity and good will of the proposer:
It is a melancholly Object to those, who walk through this great Town, or travel in the Country, when they see the Streets, the Roads, and Cabbin-Doors, crowded with Beggars of the female Sex, followed by three, four, or six Children, all in Rags, and importuning every Passenger for an Alms.
Swift's proposer-persona is a man who is horrified by the sad sight of destitute mothers and children, and the reader is lulled into the belief that what follows will be a considered, humane solution to this sad problem. In the first few lines, then, Swift has created a person who is sympathetic and reasonable and, more important, may have a solution to these tragic scenes.
The proposer's logic and economic expertise are further established in the next few lines:
It is true a Child, just dropt from it's Dam, may be supported by her Milk, for a Solar year with little other Nourishment, at most not above the Value of two Shillings, which the Mother may certainly get, or the Value in Scraps, by her lawful Occupation of begging, and it is exactly at one year Old that I propose to provide for them.
Among other things, this proposer can be characterized as a thorough and careful economist who has performed objective, not sentimental, analyses that lead him to create a model for solving this economic and human tragedy. At this point, even a careful reader has no clue where this proposal is heading, but reader senses that this proposer is intelligent and reasonable.
Not only has the proposer done his economic homework, but he has covered the religious and political implications of the problem:
it would greatly lessen the Number of Papists, with whom we are Yearly over-run, being the principal Breeders of the Nation, as well as our most dangerous Enemies, and who stay at home on purpose with a design to deliver the Kingdom to the Pretender.
If the economic and humane aspects of the proposal fail to convince the reader, this proposer understands that his readers can be persuaded on the basis of the plan's ability to get rid of Britain's enemies. Because England is a Protestant country that is faced with an Ireland overrun with Catholics who may try to assist a Catholic king (in exile in France) to take over England, the proposal has the important additional benefit of ridding Great Britain of Catholics, who are the natural political enemies of the English.
In sum, then, the proposer is not only characterized by his humanity, objectivity, and economic expertise but also by his patriotism and awareness of the political dangers that threaten the continuation of English life. If one ignores the fact that children are being eaten, this proposal has a lot of merits.