But copyleft licenses do end up preventing software from running on some platforms. For example, none of the work that goes into the Linux kernel can be made available to Windows users.
I'm sure the FSF sees this as a tradeoff that has to be made in order to keep free software viable. But that's a very different story than "user freedom is everything".
Well, that's right. The GPL is designed so that you can't copy-and-paste GPL code into a closed-source project. For software competing with each other, that stops the arms race being won by the side that can use their own work, and the work of the other side.
It is certainly fair in the sense that the Linux or BSD kernel people will never get to see, and benefit from the NT code, but microsoft and Apple can certainly use any BSD or MIT licensed code they want to.
But using Linux kernel code in the NT kernel is a special case of software sharing that can only be done at the source code level, by experienced programmers. And then it has to be released by the project maintainers, in this case the linux foundation, or microsoft.
But application code (e.g. an mp3 player), can be released for both windows and linux whether they are closed-source, or GPL.
The kernel might not be the best example to make your point.
> I'm sure the FSF sees this as a tradeoff that has to be made in order to keep free software viable. But that's a very different story than "user freedom is everything".
That presumes that the FSF's tradeoff is getting things wrong. If this strategy is what results in maximum overall user freedom, then that is exactly the strategy you have to follow if "user freedom is everything".
It is meaningless to say that making slavery illegal is a tradeoff that has to be made in order to keep a free society viable, but that is a very different story than "human freedom is everything". Yes, human freedom is everything, and that is exactly why we restrict people from owning slaves, there is no contradiction there.
What do you mean? The Linux kernel could theoretically be available to Windows users. In practice, embedding parts of the kernel in Windows under the license provisions of the Linux kernel is something Microsoft is unlikely to want (which makes sense because of their business model). Note that a lot of Free software does run on Windows, so the problem is not about Windows as a platform.
This is not inconsistent with "user freedom is everything".
I'm sure the FSF sees this as a tradeoff that has to be made in order to keep free software viable. But that's a very different story than "user freedom is everything".