It is how it's supposed to work. `unsafe` is intended to be used on functions where the caller must uphold some precondition(s) in order to not invoke UB, even if the keyword is not strictly required to get the code to compile.
The general rule of thumb is that safe code must not be able to invoke UB.
Yes. I was objecting to the parent poster's "can and should be" which sounds like they think people just randomly choose where to use the unsafe decoration.
The situation seems reminiscent of "using File::open to modify /proc/self/mem". It's safe to work with files, except there's this file that lets you directly violate memory safety.
I can't say I got the same feeling. To me, the "Functions like that" lead-in indicated the opposite if anything since it implies some kind of reasoned consideration of what the function is doing.
The general rule of thumb is that safe code must not be able to invoke UB.