Traditionally, higher education has been a luxury - something for wealthier people, and wealthier countries. Over the last 35 years, however, it has become more of a necessity. Whatever their income, people are getting more of it. Countries today are sending a higher percentage of their youngsters through higher education than countries with the same GDP level back in the early 1970s. People think of the US as the leader in higher education, but in fact countries like Korea and Japan have higher penetration: modern technology needs well-educated workers.
And countries with higher proportions of young people have higher life expectancies. Maybe it's just that richer countries can afford more education and more healthcare. But there's more to it. After the collapse of the Soviet system, Russia's GDP nosedived. So did life expectancy. But the life expectancy of university graduates continued to rise. Perhaps education helps people to deal with changing events.
The link between education an longevity has another aspect. Inequalities in GDP between different countries haven't changed much since the 1970s. There has been a slight narrowing, but a gap between rich and poor persists. However, even the very poor are now getting more education, and living much longer than before. And people value life very highly: when you take that into account, world inequality is much less than the GDP figures suggest.
With graduates earning more and living longer, there are certainly gaps, even within countries. But you don't close that gap by taxing graduates. Higher education delivers a good return on investment: you want more of that, not less. And the way to create a thriving education sector is just the same as for other sectors, be it manufacturing, utilities, telecoms or transport – end the state monopolies and let competition flourish.