If you believe it's still neccessary to keep sending letters across the world a neccessity, well, then we could only allow thin letters that can not hold anything else than a written letter - no items, what so ever.
Your original message seemed to express concern that the original purpose of the rules for international shipping was to support people in poorer countries?
If this cross-subsidisation is removed, then people in poorer countries will pay more and people in richer countries will pay less to send stuff to each other. That's simple arithmetic.
And I was wondering how someone could simultaneously support such a policy while expressing concern about access to international post in poorer countries.
It was definetly not designed to be abused by the world's biggest companies to be able to ship stuff for near zero cost world-wide. If you can't see how it's clearly being abused, I don't know what to say.
A trade union created in the late 1800's that made sense then, may need a change now. Although alot of damage is already made.
The problem is not physical letters, it's the postage of goods across the world, being cheaper because of subsizidies.