What are your thoughts on people who enforce their vegan diets on their pets?

Should it or would it be considered a form of animal abuse? Can a carnivorous animal like a dog or a cat really live a long and healthy life while living on nothing but rabbit food? Wouldn't these animals be dangerously underweight or weak and listless on such a diet? I don't know much about the effects of a vegan diet on animals but that shit just don't sound right...