This is pure conjecture on my part but I'm assuming the dog was put outside out of fear that it might attack or harm the baby. If the fear was legit, then the couple should have gotten the dog adopted into a new home. I know that my wife did not want a dog in the house when our children were small. I disagreed with that but waited for the children to get older before getting a dog, as I did not want to deal with a situation like this, where the dog would be forced by my wife to live outdoors.
I grew up with dogs and cats since I was a baby and I think it's healthy for children to have pets around. But others evidently disagree.
Another friend of mine has a golden lab named Ranger. They had a son 7 months ago. When the baby falls asleep on the floor the dog curls up around him. Once again I feel sorry for someone that might want to harm that child.