Not every communist is against free trade. Marx himself has a very clear position regarding the struggle between Free Trade and Protectionism that arose in Europe and America in the middle of the XIX century. About Marx's opinion on free trade, Engels wrote:
"... To him, Free Trade is the normal condition of modern capitalist production. Only under Free Trade can the immense productive powers of steam, of electricity, of machinery, be full developed; and the quicker the pace of this development, the sooner and the more fully will be realized its inevitable results; society splits up into two classes, capitalists here, wage-laborers there; hereditary wealth on one side, hereditary poverty on the other; supply outstripping demand, the markets being unable to absorb the ever growing mass of the production of industry; an ever recurring cycle of prosperity, glut, crisis, panic, chronic depression, and gradual revival of trade, the harbinger not of permanent improvement but of renewed overproduction and crisis; in short, productive forces expanding to such a degree that they rebel, as against unbearable fetters, against the social institutions under which they are put in motion; the only possible solution: a social revolution, freeing the social productive forces from the fetters of an antiquated social order, and the actual producers, the great mass of the people, from wage slavery. And because Free Trade is the natural, the normal atmosphere for this historical evolution, the economic medium in which the conditions for the inevitable social revolution will be the soonest created -- for this reason, and for this alone, did Marx declare in favor of Free Trade."
History shows us that this process had not yet come to an end. The expansion of productive forces under the capitalistic mode of production organized as a free-trade system (combined with protectionist measures, but these are secondary) had not encountered an unsurpassable barrier so forth; it is now present in each and every place of the so-called civilized world.
Knowing that continuous expansion is the very essence of capitalism, I only wonder to where it could expand further.
Well...what about China? That country has a little less than a fifth of the world's population, so probably we'll have to "endure" at least a few more decades of Liberal arrogance... :-(