It's not as simple as thinking in terms of those first order effects. Mailing subsidies reduce the cost of non-local alternatives for goods. It can often make it impossible for small businesses to exist in less urban environments and can lead to downward spirals where rural communities are self-exterminating because processes like this consistently siphon money out of the local economy.

Imagine if shipping of all consumer goods were made free. Amazon would be INCREDIBLY more dominant. And in fact, this is a large reason they started with books. The USPS has a special program built for a world 100 years ago called Media Mail which allows you to ship books for next to nothing. It made it impossible to run a bookstore profitably. Removing shipping subsidies to rural communities may very well create more of them and will definitely make them more resilient.