> The GPL does the exact opposite of copyright; the fact that it uses copyright to achieve that is just an implementation detail.
> If you believe information should be free to share and remix, you would believe that copyright infringement is not theft
No, this is absolutely incorrect. GPL requires copyright (or similar mechanism) to function. Without copyright, anyone could take the GPL'd code and release a compiled binary without releasing source. Releasing the source is the "payment" for being granted a license to copy the original code; without releasing the source, you are in violation of the author's copyright. No one who wants to use the GPL to protect their and their users' rights would advocate for eliminating copyright, because the GPL's goals cannot be achieved without copyright.
> If you believe information should be free to share and remix, you would believe that copyright infringement is not theft
No, this is absolutely incorrect. GPL requires copyright (or similar mechanism) to function. Without copyright, anyone could take the GPL'd code and release a compiled binary without releasing source. Releasing the source is the "payment" for being granted a license to copy the original code; without releasing the source, you are in violation of the author's copyright. No one who wants to use the GPL to protect their and their users' rights would advocate for eliminating copyright, because the GPL's goals cannot be achieved without copyright.