I'm in China where all of Google is blocked, including the Google Ajax library.
I use Resource Override (not affiliated!) to override this URL to a local copy of that script, so all Stack Exchange sites worked well for a while.
Some time ago, however, the red banner showed up again. It took me a quarter to realize that there's another version of jQuery loaded from Google:
So I overrode it again.
It would have taken only a few seconds if the failed script was told to me. I propose that whatever failure in loading pages, sending Ajax calls, etc., be displayed in the F12 Developer Console. This will be very helpful.
First, it saves time an interested person needs to find out what's going wrong.
Second, the majority of Stack Exchange visitors go to Stack Overflow, the majority of which are developers who know and are interested in debugging, especially in this very case where Stack sites only malfunction in known ways. I wouldn't propose the same to Google, because their users are not primarily developers.