I don't see how that's true. Let's run through the standard example from Wikipedia.
1) England can produce a unit of cloth for 100 units of labor, and a unit of wine for 120 units of labor. Portugal can produce a unit of cloth for 90 units of labor, and a unit of wine for 80 units of labor. Portugal has absolute advantage in both goods, but England has a comparative advantage in cloth. By the standard Ricardian argument, we get lots of trade and happiness.
2) Now let's change the situation slightly. Replace all occurrences of "units of labor" with "units of capital", and assume that capital can move freely between countries. We've lost the key component of comparative advantage, the idea that producing a good forces you to "forgo" producing some other good. Everyone just produces everything in Portugal, and England dies. Whoops!
3) Now allow England to set up protectionism, so that all wine consumed in England must be locally produced. This way it can survive. Not very nicely, but between (2) and (3) I'd choose (3) every time.
Am I missing something?