Why Gulliver felt despair from his journey to yahoo?

Through the Yahoos, Gulliver has come to see some awful aspects of human nature, and Swift has shown his readers what they would be (and often are) without the intelligence and graces of which they are capable. Gulliver seems willing to turn his back on the English people in favor of those he deems better than the English. Now that he has been exposed to many alternatives, he can think carefully about who to admire and what political systems to favor, and the English certainly come up short in relation to the Houyhnhnms.