Clearly from the postings above you can see that it is always situational. Sometimes an animal is better off elsewhere. This is not the same as dumping them at a shelter. You are actually placing them in a new home, ideally one you've checked out and feel strongly that is is a better situation. You are not wrong for keeping a dog to the end, that's what most of us expect to do. But when many of us take on new animals to save them from uncertain or grim futures, occasionally you are going to get in a position where one of your pack needs a different situation and finding it is a better thing to do.