Not saying you are but that line is usually used by the animal rights, PETA, anti milk, vegan crowd as to why we shouldn't drink milk.
We are also the only species to eat protein powder, take fish oil and vitamin tablets, eat tofu, BBQ a steak, dive a car, use a mobile phone, chat on forums, ect. But it only seems to be brought up as a reason why we supposedly shouldn't drink milk?
In any case if given the chance other animals will drink milk into adulthood, they just aren't as smart as us.