Again, this seems like a commonplace to me. Why couldn’t Marx recognize, like anyone (regardless of their political thought) can, that if people won’t accept their government’s money the country is in trouble?
It’s a daunting task to read all of Marx to see if he said such a thing. Instead, you might send Rogers an e-mail and ask him for the citation.
Here is a short commentary on Marx’s theory of money:
http://internationalviewpoint.org/spip.php?article286
