Because you can't compete with Chinese sweatshops. Free trade =/= fair trade
The consequences of reversing our trade agreements is that everything we got cheaper from third world countries is suddenly being made by American workers whose labor is more expensive. If you can pay a Bangladeshi 1/5th the federal minimum wage to make t-shirts, expect that your t-shirts are going to cost a lot more if made in the US.
Not only that, but everyone who could have been working in a more lucrative service-based job (which the US is better at than any other country) is now suddenly under-utilizing their potential, meaning our economy takes damage.