Delivery of mail is not a public good by the economics definition used in the Wikipedia article:
(1) A provider of postal services can exclude you from either sending or receiving mail. (Excludable)
(2) There's only a limited capacity to send mail at any given time. The postman can only carry so much. (Rivalrous)
(Of course, sustained high demand for mail delivery services can lead to an expansion of supply, ie they can higher more mail man. Just like sustained high demand for bread means more bakeries will produce more bread.)
That postal services charge the sender rather the receiver is mostly incidental and not important for the distinction. They could just as well charge you for receiving mail. Similar to how people in the US seem to pay for receiving calls on their cell phones (I heard).
Your own logic is falling apart as you used the example of military as a public good (which it is). However, it doesn't pass your test.
(1) The military can main it's own people, excluding them from receiving protection. They can also choose not to enter an engagement, leaving US citizens behind. (Excludable)
(2) There's only limited military at any given time. If every other country in the world started attacking the US, we would reach our limit to protect everyone. Probably why the uber-wealthy have private security forces and private islands. (Rivalrous)
You are somewhat right. Those very arguments are brought up on the Wikipedia page:
> Some question whether defense is a public good. Murray Rothbard argues:
>> "'national defense' is surely not an absolute good with only one unit of supply. It consists of specific resources committed in certain definite and concrete ways—and these resources are necessarily scarce. A ring of defense bases around New York, for example, cuts down the amount possibly available around San Francisco."[14]
> Jeffrey Rogers Hummel and Don Lavoie note,
>> "Americans in Alaska and Hawaii could very easily be excluded from the U.S. government's defense perimeter, and doing so might enhance the military value of at least conventional U.S. forces to Americans in the other forty-eight states. But, in general, an additional ICBM in the U.S. arsenal can simultaneously protect everyone within the country without diminishing its services".[15]
Basically, 'public goods' are an important concept, because standard economics suggests that anything that's not a 'public good' can be better provisioned by private, profit seeking actors.
The argument we just brought might suggest that we should privatize the military as well. I did not want to make that argument here, but it's perfectly cromulent.
In practice, how much a given good is a public good is a matter of degree and context.
In most context bread is less of a public good than defense.
But with sufficient effort, you can exclude people living in the same country from defense. Whereas there's little effort required to exclude people from eating your bread.
Similarly to make eg the benefits of nuclear deterrence rivalrous, you need lots of effort or extreme scenarios.
If you have a good or service with a large fixed cost, but a low variable cost, you can discuss about how much it makes sense to treat it as a public vs private good. For example, software or intellectual property in general has almost 0 variable costs, but copyright is a legal invention to make software excludable.
Networks are in-between: the postal service or the phone service or even buses or planes on a schedule have large fixed costs, but when below saturation, they have low variable costs.
I suggest we treat the postal service like we treat buses and planes.
- I get important documents (mail) all the time that I didn’t pay for.
- The postal service can also be used by millions of people at the same time. It happens every day.
Sounds like we agree that postal service is a public good.