“If you don’t know that free trade is conservative, ie, freedom enhancing, you don’t know much about being a conservative.”
You missed my tag line.
Karl Marx was a minor classical economist in the line of Smith to Ricardo to John Stuart Mill. He naturally favored free trade which was one of the earliest classical ideas shown by David Ricardo. [Some what like one might argue Keynes was not a Keynesian, in some sense Marx was not a Marxist.]
Marx was of course wrong on capital and many other of his ideas. Economics at that time was trying to understand value theory and Marx’s idea was one of several dead ends or incomplete answers. None of Marx’s mistakes transfer to David Ricardo from whose writings Marx learned that free trade was wealth and welfare enhancing.