Over 200 years of constant movement forward in time.
Historically we never "needed" free trade in any way, because we were living in a convoluted economic system in which we were exploiting most of our workers anyway (slaves in the South, Chinese coolies in the West, Irish immigrants in the coal mines of Pennsylvania and West Virginia, young Eastern European and Asian girls working in sweatshops in Northeastern cities, etc.).
Because we've eradicated all those practices here in the U.S., we have to figure out some other way to make our system work. All we've done is exchange our exploited labor for someone else's.