This does not make Rust less safe. The capability to use assembly is already there: either by using the existing assembly syntax, by linking to C code, or by linking to assembly routines directly. In order to use this, you need to use the unsafe keyword in order to indicate to Rust, "I am aware that the guarantees that Rust provides to me are not applicable when using this feature." This is true of all the existing ways of interfacing with non-Rust or assembly code, and it does not change with this new syntax.