How do you characterize the tone in which the speaker makes his proposal?
The tone with which the speaker makes his proposal is fairly matter-of-fact. He does not sense the irony of calling such a proposal -- one in which he suggests that the poor Irish acquire an additional source of income by selling their one year-old children to the wealthy English as a food source -- a modest one. It is a very bold and pretty offensive suggestion, but the speaker does not see this, and he presents it as though it only makes sense. In fact, his tone is somewhat proud, as though he has solved a problem that no one else has been able to correct.
The speaker presents his argument in a logical way, a manner that shows his absolutely seriousness and a complete lack of irony. However, because we understand the immodesty of his proposal, as does Swift, dramatic irony is created: this is when the audience knows more than the character. We know that his proposal is awful and disgusting and callous, but, to him, it is logical and objective.