Well easy to say, but if you are working in the real world, then unknown callers may be important - i.e. FedEx trying to push your package through the customs and if they can not contact you, your package goes either back or is destroyed.
I certainly don't. Every call I get from the school seems to come from a different number. And the camp she was at when she hurt her leg and had to be taken for immediate medical attention.
I get it, in your world, in your experience, it all works out. But in mine, it just doesn't. From experience, I _know_ this is true.