Another ID the story thread

Asking on behalf of another person:

In one story, two geologists discover an opening to a subterranean world when they come across a ventillation shaft that leads to a giant air processing facility that provides air for a race of creatures who are similar to humans only they do everything crazy and backwards. The opulent women used products and treatments that make them look hideous, because they think it is beautiful and the lower-class women were gorgeous because they couldn’t afford the treatments. They drive these little vehicles wildly about wherever they please, often crashing and dying. They wage wars with fantastic machines that shake the Earth above (origin of most of our earthquakes) and they have a theater where people can watch the wars in VR. The main charachter is captured and they try to execute him with a death ray but it doesnt work on his physiology so instead he is adopted into their society and actually thrives. He gets a job running the air handler facility and eventually discovers that one forgotten valve can shut air off for the entire subterranian world. Using this valve, he creates a tragedy which he ‘saves the world’ from and becomes the leader of the underground people. He eventually tires of the madness of the underground people and shuts the air valve off and leaves, returning to the surface with his friend. His friend had a similar experience that wasnt elaborated upon, as they were separated by a cave-in at the beginning of the story. His friend went on to become the leader of the rival clan to his own people and after they discovered each other they sent coded messages to one another and met up and played their people against each other to bring peace which ended up driving everyone crazy because they loved war so much.

Sounds like Hidden World by Stanton A. Coblentz.