Of course IANAL (je ne suis pas avocat). But in the end it may not matter. While GPL2 says "You are not required to accept this License, since you have not signed it. However, nothing else grants you permission to modify or distribute the Program or its derivative works", if a French court decides that if someone modifies and distributes a GPL covered work an enforceable contract is formed, it seems that the effect is the same: they have to comply with the terms.
It does matter: you can no longer sue for copyright violation, you can only sue for contract violation.
If you violate a contract, the court will order compensation calculated to "make you whole" again - to restore things to how they would have been before the contract was executed
The author seems to think there may be some issue for a writer of free software to demonstrate that he had been harmed by the violation; which wouldn't be an issue in a copyright suit. Well, at least here, copyright violation carries statutory damages.
One of the strengths of the GPL is that companies don't like it for some reason. Since they don't like it, you can offer to sell them different licensing terms. That is what the damages are. It's not $0, it's all the money you missed out on from not being able to license your project.
They do but not doing so is a breach of contract not a copyright violation.
What (at least in the US) makes it a copyright violation is the clause in the GPL contract which causes a automatic termination, and in turn makes you end up without a (previously existing but breached) contract granting you usage rights. Which then can be used to sue you based on copyright law.
But everything which causes the then not to be reached causes you not to be able to sue based on copyright but only based on breach of contract.
Through in practice this kinda could make a lot of copyright/licensing a joke (not just for software, but also e.g. art, movies etc.).
