I do think that's incorrect, but there's a broader picture issue that makes this irrelevant: Why does it even matter?
You're misunderstanding the original argument. Of course it's possible to make some money for selling something that is free. Specially if you convince people that it's not free, and that you'll go to jail if you do otherwise. But what they mean with "there's no market value", is that it doesn't create any new value to the economy. It's just money changing hands. If you ask me for 5 bucks and I say "yes, of course, no need to pay me back", we didn't just magically create value in the economy because I payed you 5 bucks for nothing. The value in the economy is the same, that's just money changing hands.
If I pay money for a copy of a song, that's just money changing hands. It didn't add any new value to the economy. If I didn't pay money for that copy of the song. The song would still be there. No change in value.
Unless, of course, if you make the argument that music would cease to exist if we start sharing it for free. Which I would honestly rather not get into.