I love the idea of a flat tax, but flat taxes don't get rid of the complexities of the tax code. The tax code is definitely full of random cruft, but the bread and butter that keeps the IRS and all those tax attorneys busy are a few principled features of the system: taxing net rather than gross income, deducting the value of depreciating capital assets over an amortization schedule, taxing income internationally, taxing capital gains differently than income, not taxing certain intra-familial transfers, etc.

Most of the complexity of tax accounting is complexity that's intrinsic to accounting itself.

NB: If you want to learn more about the theory of the U.S. tax code, I can't recommend this book enough: http://www.amazon.com/Federal-Income-Taxation-Concepts-Insig...

A flat-tax based on gross income would be unworkable. Wal-Mart has an operating income of $27 billion on $476 billion in revenues. A 5% flat-tax on gross would wipe out almost all of their profit. Apple, in comparison, has $52 billion in operating income on $182 billion in revenues. A 5% tax on their gross would leave them paying less than what they pay today.

I recommend that everyone read up on the basic mechanics of the U.S. income tax: http://www.amazon.com/Chirelstein-Zelenaks-Taxation-Concepts... (this book is very approachable, and quite short). Things that seem like "creativity" if you're not actually thinking, actually fall out from the mathematics of what you're trying to tax: gains in wealth over time. Things that seem like unnecessary complexity arise naturally in response to the challenge of sampling a continuous function (the value of assets) at discrete points (yearly, or at the time of sale).

The bones of the tax code are pretty elegant. It's complex, but it's complex because accounting is itself very complex. But nobody argues that the complexity of GAAP is a form of corporate welfare. Yes, there's nonsensical cruft layered on top in the form of tax breaks, but those are actually pretty simple in comparison.