alt Hacker News> but the only thing that protects Free Software (open source) is copyright law.
Can you elaborate on that? I have done a lot of open source (professionally and in my free time), and I don't see it.
I have exactly one example where I see that copyleft is useful, and that's Linux: it is nice to be able to get the downstream kernel. I genuinely don't have another example.
For smaller projects (even not that small actually), my feeling is that a Copyleft licence is just an opportunity for a competing project to come with a permissive licence. It happened to me in a library I built: people complained about my choice of MPLv2, eventually someone started a competing library with a permissive licence and everybody jumped on it.
An example of a not-so-small project I have is Ardupilot: as a user I love that GPLv3 should make it possible for me to access (and reflash!) it, but it seems to me that the GPLv3 was clearly an opportunity for PX4 to gain traction (Ardupilot even got evicted from Dronecode).
So yeah, I totally understand the appeal of copyleft in theory, but in practice I'm a bit more skeptical. And I say that as someone who actually licences my projects as copyleft.
> people complained about my choice of MPLv2, eventually someone started a competing library with a permissive licence and everybody jumped on it
Just because you choose copyleft (even weak copyleft like MPLv2) doesn't mean your project will succeed or be more popular. A lot of people (and especially a lot of companies) do prefer permissive over copyleft, and that's because they can built something proprietary on top, without being forced to give back. That's why they're ultra billionaire rich, and in comparison you're poor.
Software often wins because it's better. Copyleft favours the collective good, permissive favours the individual greed. In any case, all of these things require copyright law.