Oh huh. This might sound silly, but your commend nudged my opinion on copyleft. My previous take was more cynical - I remember, ages ago, seeing a lack of enforcement around some less popular gnu / fsf software.
IMHO copyleft is mostly about the balance between hardware manufacturers and free software.
It's important to remember that. It forces the hardware vendors to stay on "their side of the line" -- or at least to give up control over any part of their product which extends into the software space. This is why it's much more important for the hardware-touching parts of the stack (Linux, GRUB, GCC) to be copyleft than the rest of the software we use.
A lot of the anti-copyleft people think only in terms of software-company/software-company interactions.
See the crud around john deer tractors. Not being able to modify your word processor is one thing, being unable to repair thousands of dollars of agriculture equipment is much worse.
Also worth noting GPLv3 has an anti-tivoization clause, which guarantees your freedom to actually modify the software in practice as opposed to only theoretically.
