> A simple example would be: if they combined my submitted code with proprietary code and distributed it disallowing modifications. The receivers of that software would not have the legal ability to modify the resultant work (not even the sections which I contributed), they would have lost that particular GPL assured freedom.
They can still get the GPLed code that you wrote, from a different source - the FOSS version of it from that same company selling the proprietary version, or from you, or from a fork that is 100% FOSS, etc. The GPL precisely makes that possible.
> Obvisouly, they may do so, there just doesn't seem to be any incentive to do so. Can you suggest one?
As I already explained, it's useful for switching FOSS licenses. For example, it is currently essentially impossible to switch the Linux kernel to GPL3 from GPL2. I think FOSS communities need to change licenses sometimes, and copyright assignment makes that possible.
I see the validity in your position too. I just happen to disagree. I hope you feel the same way.