I'd support a National Retail Sales tax on a couple of conditions.

It's the same for EVERYONE! No special interests or various levels of taxation.

And not any of the following can be taxable:
1) Housing
2) Medical
3) Food

These are the 3 Biggies that everyone needs and most people can least afford if they are on a tight budget, they won't buy what they won't need unless they are irresponsible and well you can't legistlate that.

State level however will always be up to locals, here it's 8.1% Sales and whatever they want to charge for Property. When they need more money, instead of passing a new tax, etc. they just tell us our houses are worth more and collect.

Good luck on this one, but people are pretty status quo and there'll be a lot of accountants, etc. out of business if something like this passed.

Even a Flat tax has its benefits, however I know they will have a multiple tier of Flat tax based on income, which is not different from the current income based tax.