I have to say that in many (most?) C-like languages the difference between variable == constant and variable = constant will be losing your data. It is not something very Julia-specific. Some programmers of the past called for something called yoda conditions, that is basically: never do variable == constant if you can do constant == variable, this way a missing = will give you a compilation time error (on most C-like languages).
Not that I do not think your cautionary tale is not useful (the existence of something like yoda conditionals corroborate it), but it is a little more general problem, and one of the few thing that make me thing if the syntax = (assign) vs == (test) thing was not a major mistake from earlier language designers.