Gulliver is a bit of a snob. He loves moving among what he calls "people of quality," and he believes that there should be clear distinctions maintained between servant and noble families. If there is mixing, noble families lose some of what makes them so gosh-darned special. At the same time, Gulliver is, himself, middle class and enjoys a certain degree of social mobility as a result of it. While Gulliver does approve of class distinctions on principle, he also appears to be disgusted enough with society that he finds the signs of high class – wealth and power – surefire proof that the nobility is greedy, malicious, hypocritical, and grasping. In other words, he makes a distinction between classy guys like Lord Munodi, who comes of an ancient family but is out of favor with the Laputian King, and admittedly powerful slimeballs like Flimnap, in Lilliput.
Gulliver's (relatively) humble birth makes him an outsider to the kinds of court structures and manners Swift wants to satirize.
No matter how different the islands are in terms of overall morality, they all maintain strict divisions between the servant and upper classes. This makes all of Gulliver's made-up islands differ from his description of England and its weakened aristocracy.