TLS chose the threat model that includes MITM - there's no good reason that should ever change. All I'm arguing is that having a middle ground between http and https would prevent eavesdropping, and that investment elsewhere could have been used to mitigate the MITM attacks (to the benefit of all protocols, even those that don't offer confidentiality). Instead we got OpenSSL and the CA model with all it's warts.
More importantly - this debate gets raised in every single HN post related to TLS or CAs. Answering with a "my threat model is better than yours" or somehow that my threat model is incorrect is even more silly than offering a configuration of TLS without authenticity. Maybe if we had invested more effort in 801.x and IPSec then we would get those same guarantees that TLS offers, but for all traffic and for free everywhere with no need for CA shenanigans or shortening lifetimes. Maybe in that alternative world we would be arguing that nonrepudiation is a valuable property or not.
It is literally impossible to securely talk to a different party over an insecure channel unless you have a shared key beforehand or use a trusted third-party. And since the physical medium is always inherently insecure, you will always need to trust a third party like a CA to have secure communications over the internet. This is not a limitation of some protocol, it's a fundamental law of nature/mathematics (though maybe we could imagine some secure physical transport based on entanglement effects in some future world?).
So no, IPSec couldn't have fixed the MITM issue without requiring a CA or some equivalent.
The key could be shared in DNS records or could even literally be in the domain name like Tor. Although each approach has its pros and cons.
On this arm of the thread we're litigating whether authentication is needed at all, not all the different ways authentication can be provided. I'm sure there's another part of the thread somewhere else where people are litigating CAs vs Tor.