There's a small group of loopholes that would bring in just as much.
For instance, my favorite loophole is the LLC trick. Most independently wealthy people use it.
Here's how it works:
You have your earnings go to a LLC. Imagine Draginol LLC. Instead of paying me, you pay Draginol LLC. Draginol LLC then pays me a dividend each year of what it collected. Dividends are taxed at the rate of capital gains (15% I believe) and do not have to contribute to Social Security or Medicaid.
The reason this never gets tackled is that rich people don't want it to be tackled. And who are people who get paid this way? What professions tend to have people who are independently wealthy? Movie Stars, Lawyers, and Sport Stars (to name 3 obvious ones).
John Edwards uses this trick and has saved millions of dollars in taxes. But I don't want to pick on him because LOTS of people are doing this. My own accountants have suggested I do this even.