Rust is a relatively hands-off style of thread-safety: it protects against data races but doesn't try to get things like deadlock freedom that other more restrictive systems require. The benefits apply when using locks, or message passing or even raw atomics (and similarly to higher level libraries like data parallelism in rayon).

However, Rust is also explicitly designed to allow access to the "raw rope" when abstractions don't cut it (or when building the abstractions): that is what `unsafe` allows.