Near the end of "A Modest Proposal," Jonathan swifts writes that his plan of using Irish children as food "can incur no danger in disobliging England"; in other words, he is sure that England will not mind if Ireland eats its babies. Swift also mentions that it would be impractical to export the child meat, because it would require salting for preservation; however, he could "could name a country that would be glad to eat up our whole nation without it."
Both of these sentences are references to the English exploitation of Ireland in Swift's times. In those days, England essentially used Ireland as a colony, milking its labor, resources and crops for English profit.
When Swift indicates that England would not mind if Ireland ate up its babies, he is really saying that England already is eating up Ireland's "babies." This is an example of irony, which is always an important element in satire.