A lot of pets do get cold in the winter (depending on how severe the winter is where you live). Cats are often indoors, but dogs need their walks, and some of them Do need to wear clothes outside. There are a lot of small breeds and short-haired breeds, and their fur isn't enough for a regular winter. Saying that they shouldn't wear clothes because it "isn't natural" is a bit silly, isn't it? It's as natural to humans as it is to them, we wear it for warmth and practical reasons too. As for dressing up pets just for appearances, I don't see anything wrong with that either as long as the pet himself doesn't mind. I've heard of pets who actually get happy when it's time for dressing up. I'm sure that there are people who forcefully make their pets wear clothes even if the pet doesn't enjoy it and it's not cold outside, and that would be cruel.
