[msebor]

Some implementations have been making a lot of effort to do just that. GCC in particular has been adding these types of checks (either as warnings or sanitizers) in recent years and although there is still much to improve I'd like to think we have made good progress.

Adding a rule requiring implementations to error out in cases of undefined behavior would be hard to specify in the standard. It could (and in my view should) be done by providing non-normative encouragement as "Recommended Practice."