It’s not fun when you own nothing and must sell laybor, but what happens when the upper-class has machines which work faster and cheaper then you???
If super-technology existed within a proletarian society, the inequality of class would extend beyond a mere social order, it would become a barberic food-chain, in which the proletarian was eventually seen as a sub-human pest.
Millions of years ago this already happened once [inequality becoming foodchain], but humans have the habbit of extincting their own food sources. Once men are more disposable sort of become food, the economic, technological supermen will probably squander “lower life forms” even more-so the before.
I see inequality as the main threat to all life on the entire earth.