These cute little things are great to have around. They are adorable because they are so tiny. They may be undernourished or the runt but that is no reason not to like them. Sure they take special care sometimes. Of course I have heard the horror stories on how animal cruelty is a factor. But to my knowledge there isn't much cruelty to it?
Even as humans we tend to sometimes go with someone that has similar height or upbringing. I guess the difference is breeding runts of the liter could cause problems with their puppies.
The Teacup Chihuahua is fairly fragile as it is but that is what I like about them.