I thought the idea with rust was that it was low-level enough that such problems could be expressed with zero overhead in an unsafe block, and then given a safe interface for users further up the chain?

There's nothing wrong with scary-potentially-misused-unsafe stuff as long as you can isolate it and therefore less likely misuse it unsafely...

C effectively is unsafe everywhere, and other languages that are safe are non-zero-overhead, or so far up the stack that they cannot be used in kernel/system level stuff.

Is that right?