Final answer:
The idea that is NOT an advantage proposed by Swift in 'A Modest Proposal' is 'improving the diets of English adults'.
Step-by-step explanation:
In Jonathan Swift's satirical essay A Modest Proposal, Swift outlines several supposed advantages of his proposal to alleviate poverty in Ireland by selling children as food. Among the options presented, the one that is NOT an advantage proposed by Swift is 'improving the diets of English adults'.
Swift's actual advantages include reducing the population of Catholics, freeing fathers of child-rearing responsibilities, and preventing the occurrence of abortions.
The proposition to improve English adults' diets is not mentioned and is incongruous with the satirical nature of the text, which aims to criticize indifference to the plight of the Irish poor.