C'mon we know this already, it's not a backdoor.

This has been known and is discussed in the protocol and forums as the trade off in ease-of-use versus validation. For people wanting security, they simply check the verify keys, warn on key change. For people who don't care as much about verifying the recipient, they don't know about the feature, and don't use it, but they still get pretty good security, can upgrade to verifying if the choose, all without having to re-key or change protocols/messenger apps.