“Private courier companies are fine to handle the lucrative parts of the [postal] business. But they have little interest in servicing remote communities, so these areas get poor or non-existent service. Similarly, leaving health care and education to the private marketplace will result in fine services for the affluent but leave many others without access to decent services (or in some cases any services at all). While this kind of deficiency is bad enough when it comes to postal delivery, it becomes downright serious in areas like health care and education.”