Are taxes
already flat?
But basically, there are SO #%$@&^in' many forms of tax, that there's absolutely no way to MAKE them all "flat". For the most part, people in favor of the "flat tax" think in terms of federal income tax only, which is our biggest form of progressive taxation. Meanwhile the country is chock-full of many regressive forms, so "flattening" the income tax would have the net effect of placing the burden far more on on those who can least afford it.
So where to next? Flatten ALL forms of taxation? Income, payroll, excise, et al at ALL levels, federal, state, and local? Um... Good luck. (Not that many of them are in a position to be "flattened" or make any difference to do so, if they hit one side or another too hard.) Remove certain taxes while balancing those that make sense to? I'll think you'll find that Republican or Democrat, NONE of them are really in favor of shrinking government. (Bush seems to be one of the fastest at expanding us, all while draining our coffers and putting it in the wrong hands for quick economic stimulus.)
Meanwhile, taxes are used for all sorts of purposes and creating all sorts of incentives, and unless we somehow could bring ourselves to remove ALL of them, going "flat" will have no purpose since we'll still have the same unbalancing loopholes as before.
The true unfortunates are those stuck in the "cracks", where they have too much money and are taxed higher, but don't have ENOUGH money--nor enough knowledge--to take advantage of all the breaks they could be. But it's not like any system could possibly be "fair" to 290,000,000 people and the myriad of businesses at the same time.
Basically, "flattening" is not only impossible to implement, but we would likely hemorrhage to death trying to implement it.