It's inhumane to kill other living beings.
Jeff has a dog that he loves and has to move, but cannot take the dog with him.
Jeff wants to relieve himself of responsibility for the dog.
Jeff puts up flyers advertising the dog for a good home.
Jeff decides to kill the dog so the dog won't starve or become a stray.
Someone decides to adopt Jeff's dog and enjoys the dog very much.
Jeff has trouble forgiving himself for killing his beloved pet.