>Users can already choose to not use proprietary software
And developers can already CHOOSE not to use GPL licenced code, this part of your argument has no point whatsoever.
The GPL licence exist to grant the right of end users to examine, modify and compile/run the source code of the binaries they recieve.
The user does NOT 'already have these rights' with proprietary software.
When a developer licences their code under GPL it means that all recipients of the code in both it's original state or modified will have the above rights.
And again since developers will be 'end users' themselves once they recieve a binary containing modifications to their code, it creates an effective tit for tat mechanism where they will recieve the source code of any modifications.
There is no 'right' taken away from 'developers', they have no 'right' to use code other than under the conditions set upon it by it's owner, this holds true for all licences.