There seems to be some confusion between economic regulation within the country and tariffs on goods coming into the country.

Teddy Roosevelt wasn't concerned about imports or exports; he was concerned about monopolies within the country.

And, the elephant in the room that only the "free trade floozies" seem to remember is that every country can impose tariffs on goods imported from anywhere. We can jack up tariffs, but what is to prevent other countries from doing the same, and starting a ruinous trade war?

Autarky doesn't work very well. See North Korea or communist Albania as two perfect examples.