The unquestioned assumption that the stock market is a source of infinite growth is both foolish and, for anyone that thinks about it honestly, very likely to be wrong.
Even if we completely disregard the fact that limitless growth is impossible on a finite planet, and that we are daily seeing more and more cases where we are brushing against our limits, the very nature of 401ks is a pretty ridiculous way to build a retirement for a society.
Putting your retirement into a 401k means that your retirement is based on the future success of the economy. Typically what you would want for retirement would be some sort of investment structure where the economy doing worse when you are older will not impact your quality of life.
But instead we have set it up so that if the economy does poorly then, aside from all the normal problems of a bad economy, suddenly an entire generation of people will lose their safety net right away.
Like so many aspects of our society, we've let irrational optimism allow us to be highly leveraged in many ways, such that small bumps along the way have the potential to drive the entire system into utter catastrophe. The fact that we respond to these small bumps today by even further leveraging ourselves means this disastrous end becomes increasingly likely.