From a reader:

Jonah,
Tsk, tsk! Don’t you remember the end of the Raiders of the Lost Ark? The
Nazis thought that they could use the Ark for their own evil tasks, but
were destroyed (or rather, melted) for their blasphemy. Although I don’t
really remember Temple of Doom too well, at the end of The Last Crusade, it
was clearly impossible for an evil person to drink from the Holy Grail
because he or she chose the chalice according to his or her evil character,
and therefore would have not “chosen wisely”.

Me: A fair point on the Ark. But I didn’t catch that at the end of Last Crusade. It seemed to me the evil guy was dessicated because he drank from the wrong cup. He should have had someone else take a sip first.