The point in this context is probably that the players actually have to get a chance to be able to choose to face the save-or-die threat, or not. Which in turn means, of course, the DM having to give them opportunities to hear about that threat first, either by research, rumors, insider information (neutral monsters they encounter in a dungeon that trade info for food and gold), the journal found on the corpse of a dead adventurer, or a first-hand example of that threat witnessed before the confrontation (evil high-priest sacrifices a victim in front of the cult's idol by casting Destruction while the heroes are hidden behind pillars, waiting for a good moment to strike, for example). There's a good handful of measures that active players can pursue to gain that kind of information before they storm any given adventure, and another few for the DM to make the information available to them inbetween. It's a challenge for the players to prepare themselves before they face ANY threat, or suffer the consequences if they haven't.