I've read through these posts, and a thought keeps running through my head. Those who seek god/king status don't want to do the dirty jobs that must be done. They use the toilet, so they need operational water treatment plants. Need TP to wipe, so need lumberjacks/tree farmers. Need paper manufacturers. They want to ride around in their limos, or drive around in their sports cars. Need gas, so oil wells, petroleum plants, and the guy selling gas at the station. Need mechanics to fix them when issues develop, or just do standard maintenance. They like to eat. That means farmers/ranchers/fishermen. You need truck drivers/train operators to deliver all of these products. Bottom line, even the rulers would be consumers.
So, since consumers need producers, the "kill off most everyone" fails from the get go. Slave labor is fine for unskilled tasks. A lot of the labor they want is skilled labor. That means training and education, which doesn't work well with actual slaves.
Having spent a couple of days thinking about, here's my thought. They want power. Pure and simple, most people run for office to become powerful, to get wealthy, to hob nob with celebrities and other powerful people. To be powerful, you need those without power. Can't rule unless you have those who are ruled.
So, what are the threats to power? Freedom. Taking freedoms away is hard. People fight back when you outright take freedoms. Instead, convince people to give up freedom, perhaps for safety sake. Guns? Take them for the sake of the kids. Free speech? Messages of sedition/treason/racism need to be stopped. Free to choose your own jobs? Maybe give free education to people, if they take vocational tests and study in their chosen field. How do they keep their power? Increase their own base by making more fans of their ruling party. Free stuff. Popular programs.
My hope, the old truism. Power corrupts, and absolute power corrupts absolutely. Infighting in the Dems. Old school vs. AOC and her Crew. New blood in the Rep party. Maybe a third party, representing the political middle.
There's always hope...