[samus]

Accessing such areas is sometimes done deliberately since programmers could rely on the OS telling them what just happened using signals instead of nuking the process wholesale. Doing it without signals is usually slow and/or clunky (null-pointer checks, read/write permissions, existence of pages), or straight out impossible.

Accessing other processes' memory is not the concern since virtual memory provides each process the illusion of having the entire address space for itself.