Undergrad: 80k Masters: 87k PhD: 114k
I think that society today needs people to do all of those things, and more. We all need to find our own place, and excel there.
I'd posit that writ large this won't actual create a functioning society. Some in society need to be content where they are because we need people to do the "dirty" jobs that others won't do.
MBA is also way up there.
not sure about medicine...
keep in mind that elite MBA, JD, and even MD programs have very high completion rates, much higher than PhDs, and that MD and JD degrees can take less than half the time. MD degrees take as long as PhDs when you factor in the residency, but the job prospects and earnings are probably much higher.
From a purely financial point of view, it just doesn't make sense for someone who already has US citizenship to do a PhD. For non-citizens, though, it can be an excellent way to get into the country (though even then, an MS is usually enough to get that first work visa).
In addition to the fact that the Undergrad may be making more than $114K by the time the PhD student has acquired a PhD, there's also the issue of selection bias. Perhaps, on average, people choosing to get PhDs are more capable than people with Bachelor's degrees. In this case, the extra degree could be absolutely useless, and yet people having a PhD would still earn more.