Cats, dogs, pretty much all mammals NEVER drink milk once they leave mom! It's not normal. And don't you think it's gross to drink someone else's milk? It's not healthy! But we all have are opinions so....
Well for a certain percentage of the human population, drinking milk was so normal as to give a evolutionary advantage to those with the ability to digest milk..... Truth is that scavengers or omnivores take advantage of whatever foodstuffs they come across. Dogs, people, monkeys, apes, etc., will all eat dairy, drink milk if they come across it, so what is normal depends on the definition of "normal". What is abnormal is the large quantity of food in general available today, which is what allows someone to follow a strict diet, such as vegan-ism if they so choose. In the past, that would have been a luxury only afforded to the most privileged. Same with a diet high in dairy or meat. Neither of these types of diets were common until the agricultural revolution of the past century or so. To me, a diet that is unbalanced, in any way, seems "abnormal" considering the evolutionary pattern of eating - a pattern of adaptability and opportunism, which is ongoing, and changing over the millennia, as is all evolutionary adaptation.