I believe over the next 100 years or so, wages globally will normalize and companies won't need to offshore jobs for competitive advantage (or competitive necessity). At that point true free trade will exist. That will require years of intelligently negotiated trade deals, not half-thought-through deals like the TPP.
Clearly we're not there yet and countries like China continue to game the system. Not dealing with that only works to the detriment the United States.
Hence the popular support for Donald Trump's position on getting fair trade deals.