After reading how much puss and fecal matter is in pasturized milk I dont drink it at all. I hear raw milk is better but just stopped drinking milk completely I've been scarred.
Most mammals stop drinking milk at a certain point in their childhood. This is how we were built / evolved.
A few others are pretty fucked up and drink it all the time despite the obvious health problems that result.
Humans are, in many respects, unique among the animal kingdom. We can actually metabolize a great many toxins, and are
likely the most diverse animal in this respect. A great example of this is chocolate, which can kill most predators if consumed in any quantity considered normal to above normal for an adult human. Basicly the quantity required to give a child a stomach ache is likely to kill a dog without a vet's intervention. Some things that we sometimes put into a salad are also toxic to carnivores, such as some mushrooms. Coffee beans are mildly toxic, also. Other less dramatic examples of commonly consumed foods that are toxic to other animals (and to some degree, humans also) include, but are not limited to, avocados, many nuts and partcularly macadamia nuts, peanuts (which, technically, are not nuts), raisins, onions, garlic, several common spices such as chives, and artifical sweeteners such as xylitol; although it's also arguable that all artifical sweeteners are also toxic to humans, by their very nature.
So the argument that humans shouldn't be drinking milk because it's not natural to drink another species' milk or beyond the age of four is, at best, lacking in scientific support.
I agree, like almost all nutritional claims, this one lacks scientific support. It's really hard (and most would consider immoral) to do a decent controlled nutritional study. Also, nobody really cares anyway, we care more about tradition and fashion than nutrition in our dietary decisions. After all we have health insurance.
That being said, lactose intolerance is really common and there are a ton of people suffering from allergies, chronic problems, that probably are somewhat lactose intolerant and don't know it. Casein has also been shown to be a strong factor in cancerous growth.
Also, you have a good point, the last 10k years have seen these primates adapt to remarkably diverse dietary sources.
For the record I'll eat anything you put on the table.