I don't know all the statistic details, but according to some people in Eastern Europe including Russia, Flat Tax has increased economic production..With that being said, I think it's too simple and unfair, and giving our government state of mind when it comes to spending it will only hurt us in the long-run, fiscal wise. If you have read our current Code, you will noticed that our system is supposedly designed to encourage and discourage certain activities, the Flat Tax will eliminate this. A middle class man, with home mortgage, medical bills that exceeds the allowable percentage of his AGI, and other deductions to lower his taxable income, will be paying more in taxes under Flat Tax given him lesser money to spend in the economy. So in theory. When you think about it, under flat tax, he cannot receive any percentage of his money back from those expenses then you add the Flat Tax he already stretching his budget thin. At least that way I'm thinking about it off top of my head without writing it out.
General Electric didn't pay a dime in taxes last year. Without looking at their financial statements, I'm guessing it has to do with "2 years back, forward 20" rules. Or whatever the name of that rule is. Our current Code allows corporations and businesses to carry losses to years they have gains either previous years or years in future to potentially eliminate all of their taxable income. Under Flat Tax, it will disappear. Any start-up businesses would find a loss in early years beneficial and when they make a profit in long-run, (assume they do in this case) then they can get out of paying taxes on the net income and escape taxable income for a couple years. Flat Tax eliminates all of this.
In my Federal Income class, I had do this case where my client owns an art gallery that was raided by the FBI and he was found guilty of selling forgery. I wrote his income into tax form, and deducted all of his expenses that were tied to producing forged paintings and running the art gallery itself. The only expense I didn't deduct from his income were the fines he had to pay as punishment from the judge. The Code allows criminals to deduct criminal activities related expenses from their taxable incomes, however, the only exception is, the criminals cannot deduct expenses related to drug running. It's very odd, but it plainly stated in our books and Codes. Flat Tax would get rid of this oddness.
My point is, I don't think our current Code is that great, but I do believe we need a tax reform and I think giving complexity of our economy and all, Flat Tax is too simple. I generally have mixed feelings for Flat Tax depends on which versions, but I'll end up rejecting it most likely. I'm for tax reform that a little more flexible. How? I don't know, I'll need a lot of beers and other stuff to stimulate my mind to come up with ideas and write a book about it. :D