Administrators on a MUSH have a considerable amount of power. With that power comes the responsibility to use it wisely, for the actions of an administrator reflect not only on himself, but on the MUSH as a whole.
Players are frequently paranoid about privacy.
If you do it regularly, even when the players in the room know you'll be entering DARK, there's less of a chance you will forget at some crucial moment. Your personal responsibility to promote privacy overrides any RPG mechanics. I cannot emphasize enough how important it is to obey the protocols for using the DARK flag. While privacy on a MUD is never, ever, guaranteed, you should do your best to contribute towards it. First of all, never teleport a player without warning him first.