Examine the novel Gulliver's Travels as a satire on humankind in general.

Gulliver's time with the Lilliputians really puts a spotlight on quite a few of humankind's flaws.  For example, the debate between the Big Endians and the Little Endians centers on which side of the egg a person should crack: it's completely ridiculous.  However, this conflict satirizes the wars between Catholics and Protestants in England at this time, making the violence seem both unnecessary and ridiculous.  Why should it affect me if you want to crack your egg on the other side than I do?  It doesn't.  Likewise, why should it affect you if I want to practice Protestantism and you are a Catholic?  It doesn't.  Humans, in general, have a tendency to fight over basic ways of life rather than simply live and let live.  A fair point.

In Brobdingnag, the king's perspective on Gulliver and his countrymen leads to some rather harsh, but fair, criticisms of humankind.  The king, having listened to Gulliver's tales of wars, religious schisms, political parties, etc., observes "how contemptible a Thing was human Grandeur."  He even makes fun of how seriously we take ourselves given how completely ridiculous we are.  He ends up believing that humankind is essentially "quarrelsome" and prone to all manner of sinful and hurtful behavior, and he refers to us as "little odious Vermin" who, frankly, contribute nothing of value to the earth at all.  

In the third book, Gulliver travels to many locations, each one satirizing humankind in a myriad of ways.  His visit to Laputa, for example, shows us to be selfish creatures who are so self-centered that we can get lost inside our heads and forget to even recognize the presence of another person (satirized by their need to have someone strike them in the face when it is their turn to speak, or the ear when they need to be sure to listen).  The experiments performed at the Academy of Lagado seem to satirize the Royal Society of London for encouraging misguided experiments that would amount to no real benefit for humankind, but that we seem to do because we forget that science should have some useful application.  In Luggnugg, he learns of humanity's error in wishing we could live forever when he meets the Struldbrugs, a race of miserable immortals who would rather die than live as they do; implication: we wish for things without considering their consequences.  

In the final book, the similarities between Yahoo and human should be a bit too close for comfort.  These disgusting creatures are the worst: they are so selfish that, even when there is more than enough food to go around, each will try to make off with as much as he or she can out of sheer greed.  They are unreasonably attracted to shiny objects and will kill their peers to obtain such an object of desire.  They are savage, odious animals that are worth little and contribute less.  All in all, a pretty harsh criticism of humanity, but not entirely without merit.