3. WA DOR publishes all sales tax rate change notices on their website. https://dor.wa.gov/taxes-rates/sales-and-use-tax-rates/local...

In 2020, there were fewer than a 2 dozen rate changes throughout the entire year at the local level, none at the state level, and certainly not any rate changes in a single tax locale occurring multiple times during the year at any level. And this was verified by running tax rate reports for the state of WA in Avalara for each quarter in 2020.

I understand the point you're trying to make, but you're not going to win this argument by making up such blatant falsehoods. (Note that I actually handle the sales tax compliance for my company, including the state of WA, and I am definitely more familiar with sales tax rate changes than you are.)

4. The Feds do not have the power to require states to join the SST as it would violate the states' right to control intrastate commerce.

4a. Zip-coded based taxation is not sufficiently granular. For example, a single zip code in LA can contain multiple municipalities. A number of zip codes cross county and state lines. (9-digit zip codes are more granular, but only areas with sufficient mail volume are assigned the extra 4 digits.)

4b. I don't know what is behind your fascination with updating sales tax rates every quarter. Sales tax rates are generally updated every few years for any given tax location. It only seems like they update more frequently than that because you are conflating local tax jurisdictions with state-level jurisdictions.

4c. I know how VATMOSS works; as I have stated elsewhere I am a tax professional and handle indirect compliance functions for my company.

There is not a single VAT rate per country; there are 3 or more rates, corresponding to the different VAT classifications of goods. Most EU countries have 3 rates; during COVID several of them had as many as 7 rates (as a result of short-term discounted rates on certain types of goods and services).

Furthermore, only a limited number of VAT-subject digital goods and services are handled by the VAT MOSS system; physical goods are not VAT MOSS eligible, and classification/taxation of physical goods is 99% of the complexity of indirect tax regimes.

Additionally, the EU is legally and structurally fundamentally different from the U.S. VAT MOSS is possible in the EU because the member nations are bound to participate in EU economic initiatives as a condition of being a member of the EU (see, for example, the issues leading to Brexit). No similar legal arrangement exists between the American states; moreover, the U.S. Constitution does not grant the central/federal government the power to control commerce within a state.

It is simply not possible to have something like the VATMOSS in the U.S. It would require significant changes to the basic structure of American government. The best we'll get is the SST, and it's very unlikely that states like CA and NY will ever agree to give up control of their own tax systems to a system run by the Midwestern and Southeastern states.

Indeed, the SST exists primarily because most out-of-state sellers to these states would not sell enough to reach the nexus thresholds and so those sales would not be subject to sales tax; the SST is the carrot to get sellers to agree to handle sales tax compliance, and that is why it is mandatory to agree to sales tax for all SST member states as a condition of using the SST. (For example, without getting into specifics, my company's sales to all SST member states combined is less than the sales to CA, or NY, or FL, or CO, or TX, or IL.)