You need a systems programming language to write safe systems. That's what Rust is. Maybe there's room for a higher-level 100% safe language. Rust would be a good language to write it in.

In the mean time, in the messy world of writing software today, one does frequently enough come across the need for new safety primitives. Things that are provably correct but which the type system of your language does not support. In these instances, unsafe lets you lower down into systems code to build and safely wrap these new components.