I have decades-long experience with C++, but not all people do, and all people ,even experienced developers make mistakes or get lazy and take the easy way out from time to time.

I think one lesson C++ could take from rust, if nothing else, is that clearly demarking unsafe code sections is beneficial in and of itself.

If Strostrup makes the claim that developers using old C features is the main security problem of modern C++ , then an unsafe keyword would guide behavior towards safe usage.

    #No "old unsafe C" here

    UNSAFE{
    #Full C++, including "old unsafe C" here
      ...
    }

    #No "old unsafe C" here


    >c++                / treat code as "New Safe C++ only", except for UNSAFE sections
    >c++ --no-unsafe    / treat all code as "New safe C++ only"  UNSAFE not allowed
    >c++ --allow-unsafe / current behavior, allow all C++ including "old unsafe C" in all sections