> The point, for me at least, is to increase the total volume of freedom in the world.
Yes, absolutely. This is something I rarely hear mentioned. Many people consider freedom only as a local optimisation problem. This is why some people argue that the BSD licence, or the public domain, is "freer" than the GPL. It's true that if you receive a program which is in the public domain that your personal freedom is maximised with respect to that current program. It's also true that if you receive a program licensed under the GPL that you have less personal freedom (you now lack the freedom to deprive others of the same freedom you received).
But we can do better than this. Freedom is a global optimisation problem. Locally optimised freedom is called divide and conquer. Copyleft is the best solution that I'm aware of for the global optimisation problem. It should also be noted that copyleft itself only needs to exist in order to "undo" the effects of copyright. Public domain would be a trivial solution to the global problem if copyright didn't exist, or at least didn't exists in its current form whereby it automatically attaches itself to anything and everything. Having a world where both copyright and trivial copying by each member of society exists makes this a non-trivial problem.
>copyleft itself only needs to exist in order to "undo" the effects of copyright. Public domain would be a trivial solution to the global problem if copyright didn't exist
This I must disagree with. In this world of no copyright, how do I prevent people from taking my code, making interesting changes to it, and distributing the binary without sharing what they did?
Copyleft uses copyright to make it against the rules to violate the user's "four freedoms". I don't know whether we'd be better off overall in a world without copyright or copyleft, but there would be no way to guarantee the freedom of your software's future users.
Note that it's perfectly possible to explicitly cede copyright protection by putting your work in the public domain even today. Note that copyleft is nevertheless much more popular for software than "raw" public domain.
Yes, absolutely. This is something I rarely hear mentioned. Many people consider freedom only as a local optimisation problem. This is why some people argue that the BSD licence, or the public domain, is "freer" than the GPL. It's true that if you receive a program which is in the public domain that your personal freedom is maximised with respect to that current program. It's also true that if you receive a program licensed under the GPL that you have less personal freedom (you now lack the freedom to deprive others of the same freedom you received).
But we can do better than this. Freedom is a global optimisation problem. Locally optimised freedom is called divide and conquer. Copyleft is the best solution that I'm aware of for the global optimisation problem. It should also be noted that copyleft itself only needs to exist in order to "undo" the effects of copyright. Public domain would be a trivial solution to the global problem if copyright didn't exist, or at least didn't exists in its current form whereby it automatically attaches itself to anything and everything. Having a world where both copyright and trivial copying by each member of society exists makes this a non-trivial problem.