Don't mistake Free Trade with Free Markets, they are not the same thing. We have free markets in America. China, with whom we have Free Trade (really we have free trade and China practices merchantalism defending its markets) has a lot of monopolies dominated by government figures so not trully free markets.
Don't mistake Free Trade with Free Markets
Ok. Then to clarify, here's the question I want answered by a free trader: Why must our tariff rates be at zero?
A Five or ten percent tariff is not a trade barrier (is one percent a trade barrier?) Would people buy less t-shirts at Wal-Mart if they were 5% more?
As we increase tariffs, we can lower income taxes, the reverse of what has happened since the progressive era.
Don't mistake Free Trade with Free Markets
Also, when I said this I was referring to the Constitutional prohibition of duties, etc. between the states.