It is also difficult because of the two tiers of labor. A farmer will try increasing wages by $1/hour, and still struggle to find enough workers. Wages would probably have to be doubled before new workers—Americans—would start to enter the industry.
I'm assuming you're implying a conversation about China and their manufacturing capabilities. But worst case scenario short of nuclear war, assuming US-China burns bridges and somehow for some reason now US is fully unable to import Chinese manufactured goods; how does this eliminate the US and all other countries from investing in an area that has now become more profitable? You could argue that prices would increase, but then again you aren't owed cheap manufacturing, and subsidies and tariffs are paid by either the taxpayer or the consumer (which tends to have a knock-off effect on the rest of economy, anyway). There was never a free lunch.