The always on glideslope failure would be much more aparent if flying manually. Any pilot would quickly realise that the G/S is centerede no matter what. With AP, however, it will be more difficult.
I have a counterexample to that theory in actual flight data. Hand-flown, high rate of descent towards....?, to "keep up with the glideslope"; - Blew the FAF alt and the thousand-foot-to-be-stabilized-by altitude and leveled off at about the same altitude as the Irkutsk A320 - a CFIT but for some visibility at 500ft AGL.
The lesson is, 1) it happens, and, 2) you cannot say to whom it will occur.
Everyone one of us who fly knows how to cross-check altitudes and distances while descending, and why. What we all think (
and know) what should have happened, does not explain people's behaviour.
Preparation, a thorough approach briefing with a solid knowledge of SOPs and PF/PM duties and situational awareness through a cultured airmanship are significant preventative, error-trapping measures, as demonstrated by the Air New Zealand B767 crew at Apia. But it can happen to anyone.
There is no such thing as a "bad apple". The "other guy" is
us, on any one day.