Without projecting human values onto a canine, all I would say is if it really doesn;t hurt the dog in clinical terms, it's up to the owners.
Afterall, who are we hurting, really?
And while I agree that is sounds strange, or doesn;t seem to serve any purpose other than a superficial, cosmetic one, we all probably live with frivolities and cosmetic perceptions, each in our own different ways and to different degrees, whether we'd like to accept it, or agree to ever admiting it.
Or looking at it differently, let's talk about clothing for dogs. Apart from protection from external environmental factors, if it really doesn;t harm the dog, and increases the 'fun' factor between dog and owner (provided the dog likes being dresses up and is in no danger of a heat stroke or discomfort), I would say, "Why not."
But like any 'deviation', if it threatens to replace a deeper, more biologically natural process and verges onto being an obsession, then i would say that it's time someone sits down and re-evaluates perceptions, beliefs, perceptions and values.
Happy HOT PINK New Year! 