I have a Whippet, he has a special coat that he must wear in the winter when he goes outside for more than just a few moments to relieve himself, to keep him warm and it works well.
My Cairn Terrier is a freeze-baby, so he wears sweaters and coats throughout fall and winter.
If the dog doesn't mind being "tortured" with being dressed up, then I see no problem. If the dog is not of your own, then I don't think it's anyone's business or right to say whether or not dressing animals up is "wrong". If the dog is happy and comfortable, like my Cairn is, then great; but if not, then the owner should take the animal's comfort into consideration over using it as a dress-up toy.