Well, the individual income tax is a separate proposal. I partially agree with flat tax, but none of the current proposals actually REDUCE the tax, but only increase it. Really we should have instead a national sales tax. That encourages savings, and then anyone buying anything is paying tax, including foreign visitors and illegals. No tax forms, either, so you dn't have to keep registering with IRS each year.
The administration overhead savings would be enormous, compared to the horror of compiling income tax returns (and I'd be out of a job, but hey -- my skills have better employments). Sellers already have the infrastructure to collect state sales tax, so the Fed portion can be a tack-on, which the states then forward to the Feds, retaining their control (states' rights). Protects identities, etc. Marvelous idea, so won't ever be seriously considered.
And, you can configure the national sales tax better, for we know the GDP. Lower prices for everyone, so the tax needn't be but say 1% maybe 3%, which is a lot of savings to a lot of people. When there's a recession and the government wants to stimulate the economy, it's far more effective to do it by reducing selected national sales tax rates, than by what we have now.
It's not regressive, because you control how much you buy, whether rich or poor. And you can have a lower sales tax rate on what poor people buy, and a higher one for what rich people buy, like we do now.
Not to mention, that's how it was done for centuries, and when a King or emperor needed to raise money, he allocated a special tax for it, so everyone knew WHY that extra money was being collected. So we could have an extra 1% sales tax nationally just for paying down the debt. Our economy is 19T annually, so we can know just how much debt and interest gets paid off, see?
So a high 5% tax on 19T is 1T, which is the annual income tax revenue collected now. If 15%, that covers all of Social Security and Medicare, too (well, a tad over that). Difference is, people not paying taxes will be, and so the per-person cost is lower, which stimulates the economy and creates jobs.
In fact, that's how you could start it, so as not to disrupt current infrastructure, to test how well it could work. Have it be 1% across the board. Use it to pay some of the interest on the debt (annual interest on our debt is 223B, and 1% of 19T economy is 190B). Then see what happens in a year, at which point the infrastructure will be added so you know costs, too. Then reduce the income taxes, and gradually replace with the sales tax, so people have enough time to find other jobs (for the entire accounting and legal industry would be disrupted, if this is done suddenly).
Cash flow would be better too, as it would be coming in daily, not quarterly.
So of course no one will want it in Washington, for they stay in power only by perpetuating our economic problems.