GPL isn't about control in the way proprietary licenses are, since it grants rights beyond what you would get with no license at all, while proprietary licenses take away rights you would normally have under copyright.
However, compared to BSD licenses, the GPL gives fewer rights to those 3rd party developers. It also gives users of the software those developers write rights. BSD licenses, on the other hand, leave it to those developers to decide what they want to give their users.
So yes, the GPL isn't about control in the way proprietary licenses are, but it is about control.
Copyright holders retain all of the power granted by copyright. The GPL grants only some of that power to licensees. A BSD license grants almost all of it.
- Only the copyright holder can effectively enforce the license on a particular piece of software
- They are in a better position to enforce the GPL than most users
And yes, the reason for the existence of copyleft is specifically to disable the powers granted by copyright that can be used to attack the users' freedoms.
The point is simply that there is a power discrepancy between copyright holders and everyone else, and that by limiting power the copyright holders are exerting control over what happens to their creative expression.
I don't really understand why this is contentious, I just see it as a fact about the GPL. The FSF routinely refers to BSD-style licenses as permissive, which means the GPL is restrictive in comparison. "Restrictive" is another way of saying "controlling".
In this context we don't consider "restrictive" as the opposite of "permissive." The ones who are trying to restrict users are the proprietary software companies. We need to use certain language to draw attention to this because proprietary software developers are trying to downplay the fact that they are restricting their users. The only reason the GPL is not "permissive" is because it does not permit them to restrict users.
This "the GPL gives developers power" is pure FUD that showed up in the 90's as part of the reactionary trantrums throw down by some BSD groupies and by ESR and his gun-toting friends who wanted to sell Free Software to the corporate world, so they corrupted the term and invented Open Source. It just so happens that developers are users too.
So, if you want to strike it rich with open core, sure, you choose a lax license, say MIT or Apache, or even better BSD 2-clause, and when the suckers have implemented all the features and ironed out the bugs, you run away with the code, sell your startup and more power to your bank account in the Caiman's. Right?
So, no. The reason why the corporate world uses the GPL instead of the BSD license for the really important stuff is because it creates a level-playing field. It is the same situation as the Cold War (perhaps you are too young to remember its lessons?): "If you and I can blow each other to bits and take everybody else with us in the process, let's stop and rather do some conquering and plundering together, shall we?" And that's exactly why the mobile space is a nasty, miserable world of patent lawsuits: There are no mutual assurances of total, generalized annihilation if someone doesn't want to play by the rules. Patents are just not it; ask the Chinese.
I won't comment on paragraphs 2 and 3, because they, to me, look more like opinions than factual discussion.
The last paragraph, similarly, IMO is not built on facts. "The corporate world uses the GPL" certainly isn't uniformly true. To mention one example: from what I can see, a C compiler is part of the "really important stuff" and clang is more popular than gcc for new developments.