Isn't there usually some kind of way to handle this? Like in a dungeon delve, generally speaking things will get tougher the deeper you delve. Or in a hexcrawl or wilderness exploration, the further you go from civilization, the greater the danger. Obviously, this is not always true... but when not, shouldn't the GM then be trying to cue the danger in some other way?
Letting a very low-level party walk up to a lich's tower that's guarded by demons and then blaming them for not being more resourceful seems pretty bad to me. What resources did they have at that level? And which of those would have somehow helped against a lich and demons?
Why not give them a warning of some sort so that they're actually making a decision? Maybe three demons manifest, and the two laugh as the weakest chases off the mortals.
Why?
There's no right or wrong answer, I don't think, because it's a matter of preference. But why do you feel that way? I can explain my feeling about it... that the real players are more important than the pretend events of play.
Also, can't some reasonable result be found that satisfies both? I came up with just one above, in a matter of a minute or so.