Except that much of the income of the wealthy isn't subject to income taxes (capital gains are taxed under a different structure) and also the huge handouts to the wealthy written into the tax code (I'm looking at you, deductability of mortgage interest).
And much of it is - take a look at AMT which reverses deductions.
The fact is: Most of the tax burden is born by a small ratio of the population. That is not good for society, as Tocqueville eloquently explained centuries ago.
You're right, it's not good that most of the tax burden is borne by such a small segment of society. Then again, that's occurs because of another problem: most of the income goes to a small sliver of the population. Bringing in Tocqueville is not really proper, as he was commenting on a society that was much more egalitarian than our own.