Refute it then. We got on this free trade suicidal band wagon big time in the 70’s. Every economic indicator shows it has devastated the middle class.
It is difficult to quantify because different countries work under different rules(for example China doesn't have OUR EPA). Because the equation has so many variables, you can't pinpoint one thing for a single cause and effect. So to make a generalization either way is dishonest. Our economy was on the track for disaster because of deficit spending, a bloated government (with too many generous pensions), too many give-away programs, and reckless spending on government projects. So, while free trade has a small part in our economic woes, it is minimal.