President Barack Obama's budget plan taxes wealthy to aid middle and lower classes

This story says:

WASHINGTON — From front to back and on nearly every page, President Barack Obama's new budget plan delivers a message that's seldom been heard in American politics for more than three decades: It's time for the rich to pay their fair share and lighten the load on the middle class. [Emphasis added]

Wait, a progressive income tax, which requires those in upper income brackets pay a higher percentage of their income in taxes, isn't a fair share? If not, then what is a fair share?