I voted it depends for the same reasons you all did. But I also do think all animals have a right to live, if that makes any sense.
Yes I know that in the case of a dog if there is a real bad injury and/or the dog poses a real danger there are not a lot of choices involved. Like when a wild animal such as a cougar attacks and/or kills. The main difference being human involvement. In majority of cases involving dogs, digging deep enough will soon reveal human cause, lack of training, abuse, bad breeding... the list is endless. What is the answer? I don`t know. But I do know in all cases, the killing of both wild and domestic animals, leave me with a terrible sadness.