I believe that Cain's tax plan is a tax increase, and especially on middle and lower income folks.
The 9% sales tax looks like the Value Added Tax that many European nations use.
I believe that the 9% sales tax could hurt consumer purchases and that the elimination of mortgage interest tax credit could hurt the housing industry. Those two things are big drivers of the economy.
It will be interesting to see if his 9-9-9 gains traction or suffers in the light of day.
I think the theory is that the less money you have the less you spend, therefore the less taxes you pay. If your income tax with holdings are less then you have more money to pay the bills you already have and a smart person would be frugile in spending habits to avoid higher sales taxes on luxury items. So the rich would be paying higher taxes on big ticket items while the middle class is paying a lower amount of taxes for middle of the road items. To me it forces the middle class to only buy what they can actually afford. The poor is even less affected because they have less disposal income burning a hole in their pocket and usually get a full refund of their taxes anyway. That's just my take on it, but none of us on here are either financial experts or have the ability to predict the future so it's all just opinions.