They will pay more because currently the cost is partially covered by the USPS. Such treaty makes sense in two cases:

- the cost of recovery is high. 140 years ago, doing the accounting for all the parcels, letters sent from France to the US would have cost and from the US to France to then "balance" the accounts would have been way higher than the recovered money from one party.

- the traffic is balanced, that is, both countries send/receive approximately the same numbers of parcels/letters each way, each year.

Once these two assumptions do not hold any more, it makes sense to reconsider the situation. This is a question of balance.

That cost is now just properly being paid by those wanting those goods. Previously that cost was being subsidized by all USPS users (and taxpayers via bond underwriting, tax breaks given to USPS, etc).

It is 100% reasonable to have to pay more for shipping when a good has to travel a farther, less convenient voyage and go through customs. Anything else viciously incentivizes overuse of transportation and puts an uncompensated load on border protection.

I would love to hear a reasonable counterpoint on this.

I've ordered a lot of things from Ali Express, most shipping from China to the US. For a few, the price of the product + shipping was less than the price of a single US stamp! It's hard to justify that ridiculous level of subsidy. I have to pay more now? Too bad.

They will be incentivized to pay for similar American goods and services which will be better for the economy in general.

The purchaser will justly pay more. Under the current system, the US tax payer pays for it.