The crux of this argument seems to be that the author interprets the "range of permissible behavior" they cite as specifications on undefined behavior as not allowing the sort of optimizations that potentially render anything else in the program moot. A large part of this argument depends arguing that the earlier section defining the term undefined behavior has an "obvious" interpretation that's been ignored in favor of a differing one. I don't think their interpretation of the definition of undefined behavior is necessarily the strongest argument against the case they're making though; to me, the second section they quote is if anything even more nebulous.

To be overly pedantic (which seems to be the point of this exercise), the section cites a "range" of permissible behavior, not an exhaustive list; it doesn't sound to me like it requires that only those three behaviors are allowed. The potential first behavior it includes is "ignoring the situation completely with unpredictable results", followed by "behaving during translation or program execution in a documented manner characteristic of the environment". I'd argue that the behavior this article complains about is somewhere between "willfully ignoring the situation completely with unpredictable results" to "recognizing the situation with unpredictable results", and it's hard for me read this as being obviously outside the range of permissible behavior. Otherwise, it essentially would mean that it's still totally allowed by the standard to have the exact behavior that the author complains about, but only if it's due to the compiler author being ignorant rather than willful. I think it would be a lot weirder if the intent of the standard was that deviant behavior due to bugs is somehow totally okay but purposely writing the same buggy code is a violation.