It is difficulty to make credible claims of subconscious influences on authors. The lack of evidence which could be adduced to prove or disprove such claims is the reason that sort of psychological analytic criticism of authors fell out of favour after a very brief vogue in the fifties and sixties. Most responsible psychologists argue that one can only understand the psychology of a patient after a protracted period of intense analysis -- simply reading one work by someone who died several centuries ago is not sufficient grounds for psychological claims.
The notion of eugenics, improving the human race by selective breeding, and perhaps selective extermination or sterilization of groups or individuals considered inferior, was conceived in the late nineteenth century as a corollary to Darwinian theories of genetics over a century after Swift's death, and thus to read it into his work would be anachronistic.
Swift was himself Irish, and wrote "A Modest Proposal" as a satire, using the technique of reductio ad absurdum to condemn the English responses to Irish poverty. There is sufficient evidence from his biography and other works to conclude that the point of tyhe essay was to make people think realistically about how to alleviate Irish suffering by repealing many of the more repressive anti-Catholic measures.