The point was that drinking milk is something humans have only very recently in our evolutionary history have adapted to doing, so we are still adapting and a lot of us can't do it very well at all.

At least, a lot of us do it a lot worst than we realize, and there are a ton of people with recurring mild digestive issues which should not be consuming dairy daily at all, but keep doing do due to the public perception that its a healthy thing to do when in fact it's not.