Copyright law is the law. Breaking the GPL and continuing to use and distribute the GPL-licensed software means violating copyright law. So I'm not sure why you'd say it's "not the law."
As noted in the article, there's a long-running problem with confusing the FSF's preferred interpretation of the interaction between copyright law and the GPL's wording with the reality of how copyright law would interact with the GPL's wording, especially on the matter of what does or does not constitute a derivative work of a piece of software.
And as noted in the article, there are potentially significant negative consequences -- including for the FSF's goals -- if the FSF's interpretation were to be endorsed by courts and applied uniformly.
