I think what this comment thread really says is that the burden of fixing mistakes in the web's fundamental design is put on the individual developer and that this is another mistake!
If MITM is a serious issue then it's an extremely bad idea to depend on individual developers of every website out there to mitigate this.
Everything else is just wishful thinking, though. Chrome cannot decide to just deprecate (e.g.) unsafe-inline CSS tags. It would break 90% of websites, and people would move to a different browser to get their websites to work.
If MITM is a serious issue then it's an extremely bad idea to depend on individual developers of every website out there to mitigate this.