Crudely put, my point was that the people who freely choose C, C++ and Javascript (and PHP etc.) are the kind of people who don't care much for quality. I understand if there are availability or historic (or even sometimes performance) reasons why someone chose a bad language, but if not I'm a bit prejudiced towards them. Erlang, in contrast to the aforementioned languages, is a language for people who plan to do things properly.
I am only saying that Mongo is not unreliable because C++ was selected; it's unreliable because of architectural choices and lack of care which may or may not have been intentional.