would be true.

Further, although Wilde and the audience are certainly aware of this, Algernon seems to live in a blissful upper-class ignorance, blaming the lower class, and their faulty example, for his own lack of morals. Moreover, when he asks, "what on earth is the use of them?" he seems to be conveniently forgetting that it is the lower classes who likely produce his clothes, grow his food, and even wait on him in his own home. They have plenty of use. Now he expects them to be an exemplar of morality as well? It's absolutely absurd, which, given the play, makes perfect sense. Wilde seems determined to point out how absolutely absurd the upper class is through examples such as these.

The excerpt you mention in your query is an ironic postscript to an exchange between Algernon and his understated butler, Lane, in the opening scene of Oscar Wilde’s play The Importance of Being Earnest.

The opening interaction between Algernon and his butler introduces Algernon as a comically arrogant, self-absorbed member of the wealthy elite. Algernon disparagingly mentions marriage, and his butler Lane replies:

I believe it is a very pleasant state, sir. I have had very little experience of it myself up to the present. I have been married only once. That was a consequence of a misunderstanding between myself and the young person.

Algernon, with characteristic narcissism, dismisses Lane and then launches into a tirade about Lane and the lower classes. Algernon whines that Lane’s views of marriage are “somewhat lax,” which is humorously ironic because it was Algernon who had characterized the institution of marriage as “demoralizing” just seconds before. Algernon switches to complaining about the lower classes, stating that they “have absolutely no sense of responsibility” and whining that the poor should set a “good example.” This is, obviously, a comedic reversal of society’s expectations and shows Algernon’s absurd level of hypocrisy.

Interestingly, Lane and another butler, Merriman, are the only characters in the entire play who are from the lower classes; the remaining cast of characters are aristocratic. The absence of lower-class characters in the play allows Wilde to create a sort of narcissistic echo-chamber where the popular opinions of the elite are recycled for comedic effect.

Much of Oscar Wilde’s play is dedicated to pillorying the hypocrisy of upper-class England, and this excerpt from the opening scene serves to cast the British elite as comically self-righteous and self-absorbed.

Lane is Algernon's self-depricating servant.  He serves as the eiron (character who thinks he is lower than he really is), a comic foil to Algernon's alazon(character who thinks he is better than he really is).

Verbal irony is key in Wilde.  So, Lane works by understatement and Algernon works by overstatement (hyperbole).  Witness the exchange before this:

ALGERNON: I don't know that I am much interested in your family life, Lane.
LANE. No, sir; it is not a very interesting subject. I never think of it myself. (understatement)

And so, after Lane leaves, Algernon delivers this mini-soliloquy/aside to the audience.  It's classic overstatement, a funny statement because we have a member of high society making a condescending remark about the lower classes, when all the while the audience knows that Algernon has very little moral responsibility himself.  He owe's money, changes his name, lies about his whereabouts.  Also, of course, it's an unmarried man giving an older happily married man advice about marriage.

Algernon is speaking for Wilde here.  The statement satirizes the elitist, self-styled, and arrogant nature of the British upper-class, many of whom would have been in the audience laughing at themselves.

From a literary and historical perspective, Algernon is in part referring to a common 19th century tendency of the middle classes to adopt a policy of what is called "Grundyism". Grundyism is perspective of life that argues how all things must be virtuous, prudish, conventional, and "in proper order".

Mrs. Grundy, from which the term "Grundyism" is originated, is the main character of Thomas Morton's Speed the Plough (1798). Her behavior and description epitomized the very values  that Queen Victoria's encouraged her subjects to follow: family, tradition, religion, virtuosity, and righteousness.

In a letter to the St. James's Gazette penned in 1890, Oscar Wilde defended his homoerotic novel *by then, a story* The Picture of Dorian Gray by pointing out how Grundyism has become a phenomenon of the middle and lower classes that loyally adopted Victoria's views of propriety.

The sphere of art and the sphere of ethics are absolutely distinct and separate; and it is to the confusion between the two that we owe the appearance of Mrs. Grundy, that amusing old lady who represents the only original form of humour that the middle classes of this country have been able to produce.

Meanwhile, the upper-class peers of a man such as Algernon Moncrief would gladly overlook Grundyism and indulge in the behaviors that directly oppose its prudish nature. This is why Algernon, an upper-class man by way of connection, expects for his butler, a lower-class man, to "set the example" of prudish behavior that is common to Grundyism.

When Algernon says

if the lower orders don't set us a good example, what on earth is the use of them

he is literally distancing himself in terms of class and behavior from the lower classes.

The "good example" refers to the previously mentioned Grundyist behavior.

The "use of them" means that the middle and lower classes have found their identity and their voice in the ridiculous Mrs. Grundy and, in order to have any leverage in society (this is  from Algernon's point of view), they might as well serve as the conduits of prudishness that the upper classes flatly refuse to follow. Hence, in Algernon's world, people like Lane are merely Grundy pundits that preach to the deaf ears of the "fashionable society".