Earlier quoted context omitted.
There should be incentives to skill development and personal investment.
Exactly what benefit to society does your taxi driver having a PHD provide?
That is an extreme example, but it doesn't really make any points.
In general, society benefits from each member striving to fulfill their potential. That doesn't mean everybody needs to have PhDs; in fact, I think more the opposite, that more people should be doing apprenticeships and attending trade schools. But in general, a society that has higher skill development will be more competitive in a global economy. That helps society as a whole, even more so in societies with less extreme wealth disparity.
I honestly don't know what you're advocating.
Are you saying some people shouldn't be allowed to get a PhD? Or that somebody with a PhD shouldn't be able to change their mind and switch careers? Or that it's a waste of time for people to pursue a PhD unless there's a direct and immediate benefit to society?
And maybe your hypothetical taxi driver's PhD dissertation actually did make a breakthrough contribution to society, but then she decided she didn't care for academia and has taken some time off to plan her next step and is moonlighting as an Uber driver in the interim. Is that enough benefit for you?
That question feels like it's making an awful lot of silly assumptions – though maybe I'm the one misinterpreting and making bad assumptions.