> The counterargument is that the massive increases in wealth inequality since the 50s - a time when the average single wage earner could afford a relatively secure lifestyle - "just happened", which is obviously rather implausible.

It's not that implausible. It's the effect of technology - not just automation / computers (only since 90s or something) but also before, we had information technology - ever since the telegraph was invented. In simple terms, it enables ever-increasing scale of human cooperation, bigger countries, bigger companies etc. so the "winners" (smartest, most experienced, most educated, most corrupt, most sociopathic, most networked, or simply those with a better starting point) win ever more, at a bigger scale.