Why are people unhappy that a political figure pays only 6 million dollars in taxes?

I am no fan of Mitt Romney.
But my grandfather, my father (both deceased), and me, all together, may not even earn 6 million dollars in our lifetime (I am working on it however), much less pay it to the government.
Six million seems like a lot to give to a greedy, corrupt, wasteful and generally dumb government.
And yet, there are those who think Romney is holding back, even though it seems he is obeying the law.
Are there that many people who are so petty, and so jealous?
People seem to be critical of Americans for being overly self interested, hegemonic, racist, povincial, etc.
But very few seem to be critical of Americans for being petty and jealous over somebody else’s income.
I think that is a bigger problem than the former category of bitching about Americans.
How much is enough?