This chart illustrating the 2005 income tax burden from the Heritage Foundation is very enlightening:
What this means is:
The top 1% of income earners are paying 39.4% of Federal Taxes.
The top 5% of income earners are paying 59.7% of Federal Taxes.
The top 10% of income earners are paying 70.3% of Federal Taxes.
The top 25% of income earners are paying 86% of Federal Taxes.
The top 50% of income earners are paying 96.9% of Federal Taxes.
The bottom 50% of income earners are only paying 3.1% of Federal Taxes.
These quotes come to mind on this aspect of heavily taxing a minority:
Milton Friedman:
"Congress can raise taxes because it can persuade a sizable fraction of the populace that somebody else will pay."
"A government which robs Peter to pay Paul can always depend on the support of Paul."
-- George Bernard Shaw
Vanya Cohen:
When there's a single thief, it's robbery. When there are a thousand thieves, it's taxation.