I agree that there should be an "are you sure?" message before you click on an enemy that would result in death. Even NetHack gives you a warning message when you attempt to walk into (i.e. attack) a peaceful NPC, who would oftentimes turn hostile and kill you. Nethack doesn't need to punish people for pressing a wrong button - it has plenty of other ways.
I also agree that the warning message you get before desecrating JJ should be removed. Let the players figure it out the hard way - of course, do let the players know that it was only misfortune on the player's part afterwards (you don't want the player to think that it happens 100% of the time).