“So you will just get an additional tax. End of story.”
That’s most certainly not the end of the story. Naturally Cain won’t sell it this way, but one of the big benefits of an additional tax is that it’ll be regressive and fall on the shoulders of people who currently have no income tax liability. Then it wouldn’t be just Fat Cats revolting against taxes. It’d put a dent in the tired “for the rich” counterargument.
But they WON’T stop the income tax.