IF what you are saying is correct, then the issue is totally between the state and the citizens of that state. And Amazon could rightly tell the state to go pound salt.
But as I said above, the law is supposed to look at the SUBSTANCE of what is going on, no matter how cutesy people try to phrase, label, or characterize it.
The law is not concerned with trifles.
And the quoted phrase doesn’t say “No tax or duty (well, we mean except for....)....”
It says what it says.
Amazon regularly tells states to pound sand. However, courts have ruled that states have the right to force companies to collect sales taxes for them; Amazon says they aren’t in the state, and if the state defines something they do as being “in” the state, Amazon threatens to remove that.
Meanwhile, if Amazon doesn’t collect the taxes, we who buy from them have to keep track of all that we buy, and file a form at the end of the year, or monthly, or quarterly (depending on your state). It’s a pain, but if we want to be good, law-abiding citizens, it’s what we do. Much easier when the tax is collected at the point of purchase — also much more transparent, because we see exactly what we owe at the time we owe it.
By hiding the tax, Amazon makes it’s customers think they are getting a better deal, because things “cost less”; only later do they find out they still owe the tax, or worse, they decide to break the law, cheat on their taxes, and then they have to live with that.