Generally speaking, continuing to kick the crutches out from under the lower classes is a bad idea especially when there are no better solutions being implemented.
You need to keep in mind that the postal treaty wasn't JUST for China either, almost every single nation was part of the postal treaty. Withdrawing from this treaty would likely result in increased postage for all international shipments.
Luckily there is a very easy way for people to avoid paying for shipping... although maybe things have changed since I was young. Shop at local stores if shipping costs make buying by mail too expensive. Like it was forever prior to Amazon.
Prior to 2005 it was consistently less expensive to shop at the local CVS, book store, or radio shack than to order online.
If my business model requires public subsidies for shipping my goods to turn a profit, my business model is garbage since 100% of my profits are literally taxpayer funded. Maybe small quantity mail order batteries from China isn't actually a reasonable thing to have and it maybe actually costs less to buy batteries in giant crates and have them available in local stores.
I might even say that this is obviously the case (for the battery example). Plus you build the local economy rather than subsidizing it's obliteration.
As a person who ran a local store 'back when', the cost of shipping was factored into the wholesale price which then was used by the store to calculate the retail price. The end result was that shipping was included in the mark up percentage, typically 60 to 100%.
If a middle man was used, like an importer/warehouser, that middle man added their markup on shipping as well, typically 20 to 40%.
The only thing I do want to bring up about shopping locally, for electronic components specifically, is that stores like Radioshack are essentially extinct, at least where I am in the Midwest. There are no local electronic stores of any variation except for Best Buy.
Which is precisely why I do not shop at corporate mega stores that make it impossible for smaller businesses to compete using shady practices to lower prices.
Once Amazon or Wal-Mart are the only company left, they will be free to raise the prices to whatever they want.
You need to keep in mind that the postal treaty wasn't JUST for China either, almost every single nation was part of the postal treaty. Withdrawing from this treaty would likely result in increased postage for all international shipments.