We do it because, as magcpen suggested, some people have severe phobias of certain creatures. We do not do it for all reptiles or amphibians, we only do it for snakes and spiders. And it is not at all meant to be demeaning, and in fact, I know some people who usually don;t go to Pet of the Day (people who generally just like dogs or cats) but DO go whenever there's a Creepy Crawly warning.