Having "unsafe" mean "can wreak havoc if used incorrectly" is fine, as long as it's clear what constitutes incorrect usage, and what the behavior of correct usa

Having "unsafe" mean "can wreak havoc if used incorrectly" is fine, as long as it's clear what constitutes incorrect usage, and what the behavior of correct usages is. And it does not have to be clearly defined what "havoc" is (just like undefined behavior can cause any behavior). My issue is with using "unsafe" to mean "watch out, you might be using this incorrectly, but no one even knows the exact rules that you should stick to to make sure your code is correct." Of course, having it be in the "unsafe" part of Rust is better than having it be in safe Rust. But ideally you would be able to look at any part of a Rust program and be able to tell what it does, without having to think in terms of specific compiler optimizations or hardware details. Otherwise formal verification of concurrent algorithms and data structures becomes hopeless.