Of course, Shakespeare is commenting on a real phenomena in English society: the exhibition of American Indians, transported back to England from the new colonies in Virginia. Elizabethan entrepreneurs quickly saw a profit in the "natural" people who inhabited the Americas. These Native Americans were brought to England and displayed for profit. Most quickly succumbed to diseases for which they had no natural immunity. But more of these natural people were readily available, and so the trade continued for some time. Stefano and Trinculo's thinking reveals them to be little more than charlatans, out to make a quick profit.
Stefano and Trinculo readily fall into agreement with Caliban and plot to commit murder because they think there is a profit to be made. But there is another reason, as well. Stefano enjoys his new status as Caliban's god. He delights in the adoration, the reversal of fortune. He has gone from butler to god and sees it as a huge improvement in status. Just as Sebastian and Antonio expect power as a reward for violent behavior, the butler and the court jester would like power with a minimal amount of effort. If murdering Prospero will make them kings of the island, they are ready to do Caliban's bidding. Of course, just as Sebastian and Antonio were being watched, so too are these three drunken conspirators.
This scene involves low comedy, the kind of slapstick that depends more on actions than words. Caliban, Stefano, and Trinculo are funny because the audience thinks their efforts ridiculous. Trinculo is dressed as a clown, and Trinculo rode the storm to safety in a wine cask. Although Sebastian and Antonio's plot might represent real danger to Alonso (if Prospero were to permit it), Trinculo and Stefano's plot can only represent impotence. Their plan to murder Prospero and ravish Miranda is doomed from the start, and the audience is always aware of this. In their drunkenness, they are ineffectual and thus can be enjoyed. In Caliban's innocence, he has allied himself with buffoons. He bribes his accomplices with promises of choice foods and is too unsophisticated to realize that these men would also enslave him if given the opportunity. Stefano and Trinculo represent the worst that civilization has to offer — debauchery and absurdity.
