Even when he's trying to be dead serious, Sinclair Lewis can't help but mock the parts of people's personalities that he finds lacking, shallow, or downright bad. When describing the arrival of a pretty young woman in Gopher Prairie, for example, Lewis captures the reaction of the town's conservative women by saying:
She was tall, weedy, pretty, and incurably rakish. Whether she wore a low middy collar or dressed reticently for school in a black suit with a high-necked blouse, she was airy, flippant. "She looks like an absolute totty," said all the Mrs. Sam Clarks, disapprovingly, and all the Juanita Haydocks, enviously. (28.4.2)
Passages like this one remind us that moral judgment is rarely if ever pure. It usually comes from a place of proud superiority or, in Juanita Haydock's case, from envy. Mrs. Sam Clark wants to think she's above dressing prettily like this new girl, but the truth is that she's getting too old to pull it off. That's why she and Juanita criticize the girl: they're secretly jealous of her beauty.
Sinclair Lewis is obsessed with pettiness more than any other human quality, and you can see it in the way his narrator takes an especially sarcastic tone toward petty characters.