We use GPLv2 licensing for substantial portions of our code beyond our Linux kernel changes. Vanadium is licensed as GPLv2. As long as copyright exists then there's a place for copyleft to counter it.
> probably to cater to it's corporate sponsors
That's a strange thing to claim about Proton and Cape. Those are the only companies we're aware of sending us any substantial monetary donations in the past couple years. It has several $10k donations from Proton and maybe around 10x that for Cape which sells phones with GrapheneOS for a $50 fee.
We have a list of formal sponsors at https://grapheneos.org/sponsors which are 4 server companies sponsoring dedicated servers, a GeoIP database company giving us sponsored access to the downloadable database and a VPN company sponsoring 2 DataPacket servers. We could list Cape too but they started donating to us on their own.
> copyright is really the only thing that protects Free Software at all
What does it protect it from? GPL is widely violated with minimal consequences. The main impact is that a lot of Android OEMs and similar companies release Linux kernel drivers as open source while the firmware and userspace drivers are closed source.
> Proprietary software can be kept secret
The source code can be kept secret but not the code running on the device. That can be reverse engineered and forked. If copyright was abolished, it would be legal to fork closed source software. That's becoming far easier to do from a technical perspective.