The bourgeoisie, wherever it has got the upper hand, has put an end to all feudal, patriarchal, idyllic relations. It has pitilessly torn asunder the motley feudal ties that bound man to his "natural superiors," and has left no other bond between man and man than naked self-interest, than callous "cash payment." It has drowned the most heavenly ecstasies of religious fervor, of chivalrous enthusiasm, of philistine sentimentalism, in the icy water of egotistical calculation. It has resolved personal worth into exchange value, and in place of the numberless indefeasible chartered freedoms, has set up that single, unconscionable freedom--Free Trade. In one word, for exploitation, veiled by religious and political illusions, it has substituted naked, shameless, direct, brutal exploitation.
Marx isn't saying protection is good and free trade between nations is bad. He's attacking what he took to be the whole "bourgeois" attitude that puts economic life and economic freedom first. It's freedom to buy and sell that he's attacking -- and the attitude that values it -- not international trade with low or no tariffs.
Here's Marx's pal Engels explaining where Marx stood on free trade in the sense of lowering international restraints on trade:
“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 fully 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.”(Engels: On the Question of Free Trade)
Marx and Engels wanted free trade because they thought it would sweep away survivals of the old economy and society and open the way to communist revolution. Sometimes they ridiculed the whole debate as a capitalist one of no concern to communists, but they generally came down on the side of free trade. They did not have a high opinion of protectionism and protectionists.
Same thing. Marx and Engels did not support free trade as a means of running the economy, only as a tool for the destruction of capitalism. The implication was that free trade was a Marxist concept. It is the antithesis of that. It is the ultimate expression of capitalism. You see I don't believe in Marx and Engels or their theories. I don't believe in their premise.
There for to say that Marx was a free tradeer is to completely misinterpret him, Marxism, and what he wrote. He was not embracing free trade for himself, he was only embracing it as a negative force.