In a short new paper, economists Gary Becker and Kevin Murphy make the case for addressing income inequality by working to lift the bottom, rather than penalize the top, earners. I suppose this is a worthy goal. In the course of arguing against steeply progressive taxes, they say:

For many, the solution to an increase in inequality is to make the tax structure more progressive; raise taxes on high-income households and reduce taxes on low-income households. While this may sound sensible, it is not. Would these same individuals advocate a tax on going to college and a subsidy for dropping out of high school in response to the increased importance of education? We think not. Yet shifting the tax structure has exactly this effect.

[Semicolon sic; emphasis mine.] This is manifestly false. Progressive taxes, penalizing high earners in every field, are presently combined with government subsidies for higher education. The typical high earners described by Messrs. Becker and Murphy are rewarded at first, then penalized; while overeducated failures are purely rewarded, and -- most crucially -- those who succeed without reaching into the goody bag of state-subsidized education are purely penalized. In short, the present situation is worse, not better, than the strawman constructed by the authors.
The crucial test of the case for more education is whether it truly increases productivity, or merely provides a credential which signals the graduate's desirability. The authors do not address this problem at all. Their graphs, while cheerfully colored, are perfectly consistent with a world in which those who were going to earn a lot of money anyway were first obliged to waste several years getting a diploma to signal their status. More government-imposed pressure toward credentials -- which will be the inevitable result of making government, rather than employers, the judge of how much education is desirable -- will only exacerbate this problem and further reduce real economic freedom.