The operations themselves may only impose a performance hit of 10% or less, but the optimizations that those checks inhibit can easily cascade into a 2x slowdown, which isn't acceptable if Rust wants to compete with C++.

As for your correlation, I care a lot about safety, but I also recognize that the safest language in the world isn't going to pose any real-world improvement if it's not capable of competing with less-safe languages in their entrenched domains.