I'm replying to the comment that RMS supports copyright. I don't believe he does, I believe he would rather it not exist at all but since it does, you have to make use of it.
That's the full context of what I was saying. Copyleft is a hack for copyright. In a world where copyright is enforced, RMS doesn't consider the neutral ground of public domain licenses (like the popular MIT and BSD licenses) good enough. They do nothing to solve the problem of proprietary software.
The GPL is entirely dependent on copyright. Rather than pretend copyright doesn't exist, the GPL turns it in the other direction. By violating the GPL, Copilot is still violating copyright.
Sure, there would be software with code not published, but if it was ever leaked which it often is, you could do whatever you want with it.
But in a world where copyright does exist, copyleft is a tool to fight back.