To me this is the fundamental issue with the friendly/boring C proposals. The whole reason to use C/C++ anymore is for performance, in return for which you are responsible for certain things - like using only defined behavior.

If you are writing e.g. crypto code, why not use a higher level language that provides more checks and guarantees, and is generally easier to reason about? Or segregate the performance-critical "engine" type code into C++ and use something higher level for everything else?