The flat taxers are just about as persuasive as the flat-earth crowd. I note even the D-G teed up Mike Huckabee editorially today for joining the flat tax crowd. (Who's advising him, anyway?) The idea resists any sort of careful analysis. Here's a good one, at the scrupulously non-partisan factcheck.org. The flat tax is a GREAT idea if you're filthy rich. Not so much if you work for a living.
How would you like to pay a 30 percent sales tax on the next F-150 you buy? That's the low end of what the real cost of a "revenue-neutral" flat tax would be.