Nothing but the law, which may not stop them, just like the law doesn't stop shoplifting. But you don't reward shoplifters with free products, you tighten your controls, and prosecute where possible. Conversely, open source = no control, i.e. no law.
The next proprietary agreement that the Chinese keep will be the first.
So your answer is GIVE it all to them, for FREE instead? Sorry, I don't normally use all caps, but since you do maybe you'll get the point.
No offense taken on the caps, use as you wish. i use them for expression and emphasis, contrary to 'convention'. Back to you on the rest of your post later.
Since you've already conceded that there is (virtually) no law involved in this issue, be it Open Source or Proprietary, your argument falls flat. It is not an Open Source issue.
On another front, For somebody who asserts a communist aura to Linux and Open Source in general, you certainly are sounding more and more like a Marxist, when you assert, as you have above that the creator of a given piece of software CANNOT do with that software as (s)he wishes, which would include liscensing it as Open Source. What other freedoms do you want to take away?