The IT side of this is often overlooked in free trade discussions. It's one thing to impose tariffs on manufactured products and raw materials, but it's damn near impossible to do anything to restrict the flow of information through electronic means.
"Comparative advantage" today is being driven by the fact that developing countries don't incur the overhead production costs that developed countries do.
The most obvious examples of this are labor forces that operate in slave-like conditions (and sometimes outright forced labor), as well as the fact that industry in developing countries doesn't have to worry about containing their industrial waste (unlike us, Chinese industries just dump their toxic waste raw into rivers or onto the ground). Furthermore, the industries in many developing economies are state-subsidized. As a result, their steel and aluminum mills can afford to overproduce at cost or even at a loss thanks to government funding, and then dump that metal onto us to undermine US domestic production.