And everyone you iMessage with? Both parties to the conversation have the plaintext and a key that will decrypt the whole conversation.
Unless you are 100% certain that everyone you iMessage with has also done this, your conversations are still not reliably private.
Even then, Apple can silently inject additional escrowed wiretap keys into the keylist for one or both participants, although this is an active attack and can be detected by monitoring changes to the keylist for a given phone number or Apple ID provided by Apple's iMessage APIs.
iMessage is not a security or privacy-first messaging app. It is a fun and usable messaging app with decent efforts towards privacy and no user tracking. The only messaging app that goes all the way with privacy is Signal, which I use for most of my communication. But Apple is focused on the user experience, and there are some fundamental trade offs with user experience that are not necessary for most users. Most users are never going to be subpoenaed by the police.
Look, iCloud Backup is the weak link here. I don't actually know if your messages will still be in other peoples' backups even if you turn off iCloud Backup, but I also don't know enough about the security model one way or another to be able to say, and I haven't seen evidence provided. I'm willing to believe that they are, just for the sake of argument.
What I was trying to say is that Apple is trying to make it as easy as possible for people to recover their messages, because this covers most peoples' threat models, which do not include protecting data from subpoena. Signal is great technology but the fact is it doesn't sync messages between devices because they haven't figured out how to do that in a way that's fully secure. This is a feature that tons of iPhone users want and are not willing to sacrifice for higher security. What am I missing?
But is this problem a problem just at the personal level? The big problem lies at a societal level. And does it then help that a few computer hackers are informed enough to make an important (and crippling) technical decision?
The problem at the societal level is that people prefer convenience to security. The number of people that would forget their password, lose their entire message history, and blame Apple for it is huge. If you have everything end-to-end encrypted, that's the support burden you're looking at, and it's absolutely nontrivial.
