CharacterCounts: The man is not being prosecuted because he failed to stop him from driving but because he assisted and aided in the drunk driving by taking the drunk back to his car.
ImphClinton: What kind of idiot takes a drunk to his car to drive home or anywhere else. This man deserves to go to prison.
Are citizens compelled by law to protect other citizens? Before you answer, read post #21
No!
Citizens are also not allowed to put other citizens at risk. This is not a case of a toll booth operator failing to stop a drunk. This guy took the drunk to his car so that he could drive.
One has no duty to stop a bank robber. If, however, you give a ride to a bank robber assisting in his getaway, knowing he is a bank robber, you are guilty as an accessory. The key element here is that Powell knew the an was intoxicated.