I'm going to go ahead and say that if (1) deciding whether code is valid for your language is undecidable, (2) no industrial compiler makes any effort to conservatively accept only valid programs, and (3) unsoundness cannot even be detected at runtime (this is true of C in the multithreaded case) and may result in completely arbitrary behavior, your language is unsafe.

There are only unsafe coders.

There are no unsafe cars, either, only unsafe drivers.

However, there also are plenty of cars that safe drivers will refuse to drive. You don't need crumple zones, safety belts, etc. in a car you will never drive.

> There are no unsafe languages, only unsafe coders.

There are no unsafe nuclear launch buttons, only unsafe nuclear launch button pushers.

Hmm, maybe some buttons should be harder to push...

I enjoy using computers because they make fewer mistakes than humans.

I would like to apply the same principle to the language I program computers in. Make it the computer's job to minimize mistakes - it might not be perfect, but it's definitely better than I am!

>There are no unsafe languages, only unsafe coders.

And who develop the languages? Coders.

Ergo, exist unsafe languages.