True, but I think allowing potentially UB-invoking code to not use "unsafe" (e.g. because the use is in the context of FFI, so the unsafety is thought to be "obvious" and not worth marking as such) might be even less advisable. This makes it harder to ensure the "social rule" mentioned by GP, that every potential UB should be endowed with a "Safety" annotation describing the conditions for it to be safe.