My argument is this: technology has been driving down the market value of human labor for the last century at least, and soon the market value of human labor will be pennies.
I specifically use market value because the market valuation mechanism is irrational and its meaning of "value" is different from what people often mean when they talk about value. E.g. the contributions of a fireman are far more valuable to a society than those of a mutual fund manager, but the market value of the fireman's labor is far lower.
Anyway I don't know when it'll happen but the cost of doing many things with AI, automation, etc will soon be very low, and having a human do the thing maybe worse maybe better, will be prohibitively expensive. Even if you argue that in the past new technologies have created new jobs, one can look at the labor market value trend of the last 70 years to see that it seems we've passed some turning point where human labor market value in emerging skillsets can't surpass the ability of technology to make them redundant - by which I mean take a look at them wages, they are slip sliding into oblivion.
Maybe not all jobs, but if even 20% of people can't justify their existence under capitalism with labor in a way that feeds and houses them, that's a historic national crisis.
Stopping technological development probably isn't the long term solution. Unions are great but also just a bandaid on a broken system - don't we want to enjoy the benefits of decreased scarcity?
It's time to start having real conversations about how to organize our society as scarcity diminishes to near 0, or if you don't like that, how to organize our societies with the expectation that 20% of people or more simply won't be able to justify their existence through labor.
If you can think of a way to make capitalism work in such a way without enforcing artificial scarcity, I'm all ears, but I'm skeptical. Probably we need to stop requiring people to justify their existence with labor and just let people have food, shelter, medical care etc in return for nothing at all. We almost certainly already have the resources to allow this, and if we don't today we definitely will in 50 years.