Frodo: It's a pity Bilbo didn't kill him when he had the chance.

Gandalf: Pity? It was pity that stayed Bilbo's hand. Many that live deserve death and some that die deserve life. Can you give it to them, Frodo? Do not be to eager to deal out death and judgement, even the very wise cannot see all ends.

-- Lord of the Rings: The Fellowship of the Ring