Not trying to be a Rust advocate and I actually don't work in it personally.
But Rust provides both checked alternatives to indexed reads/writes (compile time safe returning Option<_>), and an exception recovery mechanism for out-of-bounds unsafe read/write. Fil-C only has one choice which is "crash immediately".
Bounds checks have nothing to do with data races. GP is right, you can add bounds checks. Either using macros or (in C++) with templates and operator overloading.
Same reason any turing complete language needs any constructs - to help the programmer and identify/block "unsafe" constructs.
Programming languages have always been more about what they don't let you do rather than what they do - and where that lies on the spectrum of blocking "Possibly Valid" constructs vs "Possibly Invalid".
