Does your wife like the dog? When it comes time to take the baby for stroller walks she can take the dog also. Great exercise for all. I have a day care in my home. I have many days when there are lots of children here, babies included plus there were 2 boxers (until the loss of 1, Loki). I think she can handle the dog and the baby just fine. I don't understand any reasons here. I've always been raised to treat a pet as part of the family. My dogs are here for good! I wouldn't get one if I didn't think I could keep it for the duration!
Your dog should provide as a great protecter to the baby! Maybe your wife should think about that.