Your comment about "nonsense" doesn't make sense.
If it's nonsense, then why are people addressing it?
He claimed that the 16th must be repealed before we could rid ourselves of the I. T. otherwise we'd have both. That's actually worse than nonsense since his (so-called) flat tax was merely another form of income tax as are all of the "flat tax" efforts and the fact that the FairTax actually rids us of the income tax when the bill is voted into law. If any flat tax were to be the tax law, we'd still have an income tax with most of the downside thereof as shown in this post.
The FairTax eliminates the income tax (and some other taxes), the IRS (and defunds it), and requires the tax records to be destroyed as well. In addition it calls for repeal of the 16th amendment (for which there is a bill presently in congress to do just that).