Imagine this. Imagine it's back before we understood as much about alcohol; about how a person's reflexes, etc., could be diminished even though they appeared fine.
Someone has drunk too much but the think they're right to drive. Someone else needs to get to the train station to catch a train for some very important purpose. So the first person offers to drive them. Person two makes the train and gets to do their very important thing. Person one has an accident on the way home and wipes out a car full of people.
Is this okay because person one had the best intentions and they didn't know at the time that it was wrong?