[catnaroek]

> After thinking about it again, unless you made an error in the specification or implementation, every programming language should actually be sound. You can always weaken your guarantees until they (trivially) hold at runtime.

That's technically correct. But it's like the joke about the mathematician who can only provide technically correct but otherwise totally useless answers.

> But that actually worries me a bit, soundness suddenly seems not such a useful concept.

Indeed, if you define soundness that way, it's a useless concept. That's why I refuse to accept a semantics that doesn't match how programmers actually think about their programs. I consider it undefined behavior to dereference a null pointer: the language implementor might trap the error to make debugging easier, purely out of goodness in his heart, but the program itself remains meaningless until it doesn't dereference null pointers anymore.

> Maybe because I am wrong with my understanding?

Nope, you're not wrong.