I know some people have the opinion that permissive licenses, or even no copyright notice at all, are better solutions to eliminating proprietary software from the world. While, in an ideal world, we would not need copyleft licenses, or licenses at all, people would simply always share the source code as a matter of custom, as a matter of simply what people do and would not even consider another course of action to be profitable or even viable, since people would simply refuse to use proprietary software, however, we do not live in a utopia where all people (or even most people) are so virtuous.
We need the GPL and copyleft licenses like it, because there are a lot of bad people out there who wish to create proprietary software, mostly because of their unrestrained lust for greed and more importantly, power over others. The GPL forces the developer to give back to the community regardless if they believe in its ethical principals or not.
That said, when we are successful, there will become a point when copyleft will no longer be necessary, but the question is, how will we know when we have reached that point? Is there a certain percentage, or even certain programs that are acceptable to be proprietary software? The point is, we are far from that threshold. New proprietary software is still being created and toted as a business model in certain industries. Some software has been commodified to the point where the only obvious solution is to use the free software, but in other cases, proprietary programs dominate.
So, if I were to make a checklist of when copyleft would no longer be necessary, it would have the following items.
1. people would refuse to invest in proprietary software it would be called, “not a money making strategy.”
2. Almost every piece of new software would be free software.
3. cars, body parts, appliances etc would have free software as a matter of course, in fact stores would refuse to sell hardware with modifiable software without the source code.
4. Proprietary software would be illegal in one or more areas of use due to the potential of exploitation of consumers.
5. The promotion of proprietary software ideology would be relegated to “fringe communities” people would be canceled, banned from most chat, forums etc for their promotion of repulsive fringe views, much like blatant racism is today (so that even someone as repulsive as Trump wouldn’t be able to stoop to it.)