Zactly! The companies involved will simply sell their wares to an intermediary who will then sell the weapons to the 'banned' countries.
If we were serious about China we'd drop them from our "most favored nation" trade status and begin slapping all their chintzy imports with higher taxes, and begin manufacturing here in the U.S. again. Frankly, I'd rather pay more for my dish towels and coffee makers than trade with my worst enemy and enhance their economy.
Free trade is the road to world peace. Wars are like rest stops. Can you hold it until we get there?