For some, mostly wealthy, mostly Republican, and mostly on the Right, there is not much to discuss regarding free trade; for them it is the default position that rarely needs defending, except to marginalize and shame heretics who might be tempted to explore the vast chasm between the orthodox
There is, of course, the cynical proponent, the paid operative, side by side with the ideologically-committed true believer. The former are less interested in the vagaries of free trade as an economic doctrine, but are determined to crack the whip of orthodoxy because they are, like the true believers, pleased to see global trade increase, but also because ever-increasing global trade contributes to what they view as the proper hierarchy of power, the one that puts corporations, the powerful men who run them, and that ever-astute risk-taking investor on top, and workers and other less morally-deserving hoi polloi on the bottom. Their incessant message is that robust and unfettered trade represents efficiency, choice, and competition, all of which we are told to crave and admire. You can't compete? Don't be weak, it's your fault anyway, so suck it up.
Having said this, it is also true that many on the Left do not have much to say about international trade, as it is currently playing out, despite bountiful data and a well-developed but under-utilized theoretical framework that vividly describes reality: unfettered, global trade impoverishes the working class and enriches (most) corporations and the managerial and investor classes.
Of course, there has been some protest against globalization. There is currently a push-back, one that may be growing, against the Trans-Pacific Partnership, just as there was against NAFTA. Nevertheless, the TPP remains a second-tier concern for the Left.
The Left finds itself once again ideologically divided, its modest resources spread thin. Protesting the ravages of aggressive trade means the Left, to some extent, aligns itself with Corporate America. If you protest, say, Chinese or Korean steel dumping in the US, you not only are taking the ostensible view of the US Chamber of Commerce (e.g., imports are fine, but only at market prices), but you are uniting with the America's economic aristocracy, largely white, Republican, and reactionary.
And this is something the Left cannot abide. It is easier to view the US as economic aggressor. With that as their default position, few are willing to rally against Chinese trade aggression or systemic Korean disregard for American patents, copyrights, or intellectual property. We see occasional outbursts against China's export quality control, such as with food additives, but that is because our health as individuals is threatened. But cheap Chinese products as a growing threat to America's economic interests? Yeah, maybe, but I have a save-a-bug rally to attend, so later, dude.
What the US does in international commerce is considered an existential threat. To report critically about what China does is effortlessly labeled as fear-mongering and bigotry. The Left will do anything to avoid such charges, so any viewpoint that might equate the two countries is embraced very reluctantly. Accordingly, we rarely see any on the Left protesting the systematic circle jerk to which China subjects American companies.
The Left wants to see other nations, at least the non-white ones, as valiantly defending their economic sovereignty. American corporations are the modern exemplars of economic imperialism. The Left too often is content to view avarice as uniquely American (or western); nations whose citizens have brown or black skin are perpetually the designated victim.
To be sure, the American Left opposes oppression of civil rights abroad, be it China, Iran, or Zimbabwe. But when they care to look at the massive, chronic trade deficits the US has with Asia and elsewhere, or when they read how corrupt officials stonewall foreign companies in China, steal technology, or hack our government's computers, the protests are muted. Instead a blame-America-first mentality kicks in. Those on the Right complain about this all the time, and they have a point.
To fairly examine East Asia's neo-mercantilist complicity in America's de-industrialization requires a willingness to confront uncomfortable realities, so most on the Left move on to something less ambiguous, like minimum wage increases, or social security. Others, of course, focus on social issues, such as gay marriage or abortion rights. The dismantling of American industry remains a low priority with purveyors of identity politics.