I completely disagree. What's the main thing the GPL does that is different from public domain or the complete absence of copyright?
It restricts how the code can be used in order to protect the writers and the consumers of the code. Without copyright and copyleft, any company can use any GPL code in any proprietary product they want, without sharing any of their changes and without even crediting the original writers. As an example, Microsoft could adopt the Linux kernel for Windows, heavily modify it, sell it, and stay completely silent about it, without any consequences. That's what a world without copyright means for copyleft.