Earlier quoted context omitted.
Few people pursuing PhDs are doing so to maximize earning potential. Disregarding the mental toll of a PhD (one problem being that too many people want to be paid to think than there are available positions), I totally disagree with the parent poster's claim that graduate school is a rip-off. Just being in an an academic environment, being able to take classes, & studying around really smart people and doing research…
The argument you put forward doesn't make sense. It's not a ripoff to make close to minimum wage for a number of years (and possibly take on high levels of student loan debt), all to work in a field where there is an oversupply of labour that depresses wages? Ok...
If you come out the other end of a PhD, then you have the opportunity for best of both worlds: high paying job to work on the problems you find intellectually stimulating.
Also, it is cliche, but doing a PhD does train a person in a way to think that you don't necessarily pick up in a normal job.