Why is Bill's favorite character King Herod?

After Bill has been injured several times by Red Chief and worn to a frazzle by the boy's inexhaustible energies and demands for attention, he has the following conversation with Sam.

By and by, Bill sits up and feels behind his ear and says: 'Sam, do you know who my favourite Biblical character is?'

'Take it easy,' says I. 'You'll come to your senses presently.'

'King Herod,' says he. 'You won't go away and leave me here alone, will you, Sam?'

Herod was King of Judea at the time of the birth of Jesus. He had been told by the three Magi that the new king of the Jews had been born in Bethlehem, where they were going in order to worship him. Herod is best remembered for the so-called "Massacre of the Innocents." In order to forestall being replaced as King of the Jews by the newborn child, Herod ordered all children two years old and under in the vicinity of Bethlehem to be massacred by his soldiers. This event is recorded in Matthew 16 in the New Testament.

16 Then Herod, when he saw that he was mocked of the wise men, was exceeding wroth, and sent forth, and slew all the children that were in Bethlehem, and in all the coasts thereof, from two years old and under, according to the time which he had diligently inquired of the wise men.

Bill, of course, is only being facetious. He is evidently a softhearted man and an easy victim of the rambunctious kidnap victim who calls himself Red Chief. However, there is a serious side to Bill's reference to Herod. If Bill and Sam were real cold-hearted kidnappers, they might consider killing Red Chief as a way of getting rid of him and saving themselves the $250 that Johnny's father demands as counter-ransom for taking the wild kid off their hands. But although both men are injured and terrorized by Red Chief, they never hurt him at all, and they would never consider killing him, even though they sign their ransom letter "Two Desperate Men." Bill and Sam can't handle this little ten-year-old boy because they can't use physical force, and they have no moral authority as adults because they are kidnappers. If they used violence on the boy, it would spoil the story by changing the reader's perception of their characters. It would also make their crime more serious if Johnny was returned home with bruises and abrasions. So Johnny can be violent with them, but they can't be violent with Johnny without risking becoming subjects of a nationwide manhunt. Their non-violence only provokes the boy to more violence.