Well I doubt the $insert_country would want to share their keys with others. Why would they? It'd make far more sense to send in encrypted message and get decrypted message back.

>The US government has shown itself to be perfectly capable of losing secrets.

But not even remotely comparable secrets. We're essentially talking about a physical item here, not a secret you can lose without losing possession of that item.

>Some proposals for encryption backdoors allow for access by law enforcement at almost any level, down to local sheriff / police

This may present logistical challenges for handling decryption requests, but I don't see it as a huge issue for keeping the keys from leaking.

Obviously I'm not actually advocating this, I just think that you're making some rather dishonest arguments here.