What he also misses: is that if I sell something to another retailer for resale (meaning he says he's going to resell what I sold him), I don't charge him sales tax on the entire purchase. Not until it reaches the final consumer is sales tax charged.
He says this isn't true, and links to a wikipedia article on a gross receipts tax. This is another confusion on his part. Some states do not have income taxes, and instead have gross receipt taxes. This is an alternative to business income taxes, not sales taxes.
The confusion is understandable. No one has ever accused the US of having a simple tax system.