I think we justify it because it eventually becomes the cheapest option for the animal. I have friends that have said if it ever costs more than a certain amount they'll just put the animal down. Usually it's in the $1500-$2000 range. Then there's the quality of life argument some people say. The animal is in pain and you shouldn't let it suffer because you don't want to put it down. How do we know the dog wanted to die too? We won't know until humans are able to bind minds to those of animals to know what they want. This is not an argument against it and I don't look down upon people that do it. I'm sure it's the toughest decision some people have to go through.