Cheap labor only gets you so far for almost all (non textile) manufactured goods. Frankly, labor is but small cost component in the over cost to make a durable good. If labor was "free" i.e. slavery this would only save 3-5% on the cost of manufactured goods. To to increase the "bang for the buck" the foreign made goods are made with cheaper materials and lower quality control in order to get the price down because cheaper labor by itself can't do it alone. This done to justify destroying the USA's industrial base.
In addition to lower labor costs and lower quality control costs, two of the big advantages to manufacturing in China or in various Third World countries is that they have negligible safety or environmental regulations, i.e. they can just dump industrial waste raw into the ground or into the nearest body of water whereas we cannot. Similarly, if a Chinese or Salvadorean worker is crippled on the job due to shoddy safety conditions, he's on his own. The reality of these additional costs incurred by US manufacturing (and that of the developed world) needs to be acknowledged through tariffs in order to make a truly level and competitive playing field