> Zeroed memory should not be particularly expensive on modern machines, because we have a lot of parallelism available to zero it off working threads.

It must be nice living a world where energy is free, you have unlimited cores and unbounded caches, and context switches, thread synchronisation and cache coherence have no cost or latency.

I'm not saying that reducing the number of cases with undefined behaviour isn't worth it in most cases, but claiming that you can just zero application memory at virtually no cost on a multicore is misguided.