I understand your point about humans perhaps being the evolutionary precedent, but what this means is we have no proof and we can kind of make it up as we go along; "humans are doing this now...we must have evolved to do it!" Personally I find discussions of what humans were "meant" to do based on evolution go around in circles and are of little relevance practically, especially since intelligence is our most significant evolved trait, and allows us to do whatever we like even if it kills us after reproductive age (eg driving cars, smoking). In our history, humans have had the intelligence to adapt to whatever food sources are available.
As far as milk being a renewable resource, it only is in the sense that cows "replace" each other on any closed farm. Once you take into account that a glass of milk took 200 litres of water to produce, and each dairy cow consumes more than 20kg of vegetable matter per day (at a feed conversion ratio of about 6 on a dry matter basis), you can see that we are squandering our resources and screwing over about a billion starving people of the world. To add to this a bit more, a kilogram of cheese requires ten kilograms of milk to produce, so that just multiplies the greed.
Basically, dairy is one of our most effective ways of saying "fuck you Somalians!"