That's a good point, but I'd actually go a step further and argue that we need to think more generally about actually defining when things should fail. This is exacerbated by a tendency of many people to actually require systems to not fail on bad input but instead try to make as much sense of it as possible so that now compatibility requires you to make the same guesses as to what the user actually meant. See, for example, the tag soup parsing of HTML (which was eventually standardized in HTML5), or the insanity that is trying to parse email messages.