There's also a reason why some people can digest milk: its a resource with nutrients and being able to intake a new source of nutrients offers a selective advantage to your offspring relative to offspring that cannot make use of these nutrients present in the environment. To say its not suitable for consumption by humans is a falsehood considering many adult humans can and do consume milk and make use of its nutrients.
You could posit this argument about anything we consume. Spinach leaves are to provide energy through photosynthesis for the spinach plant, and technically should not be suitable by consumption by adult humans so to speak if we took your logic to the limit. The fact that we have experienced gain of function mutations that allow us to digest spinach and recieve some nutrient benefit from it mean that we are able to take advantage of this resource. Milk in this sense is no different, even if not all of the human population has recieved this gain of function mutation of lactase persistance.
In biology there is no 'suitable' or not especially in the human sense of things being properly defined into discrete categories of expected outcomes, only what is physically posible through thermodynamics. If you physically can extract energy from plants, meat, milk, dirt, whatever, then its all suitable for consumption. having an enzyme to digest this sugar is no different than having teeth fit to grind down fibrous plant matter, or teeth strong and sharp enough to cut through cartilage and sinew.
You are speaking theoretically. That milk was necessary for survival by a small population of humans may have been true aeons ago during some ancient famine. This is not the case right now.
To say that humans can take nutrition from a substance is an argument that there is no criticism of the substance is a bad argument. Humans take energy from pure sugar, or taco bell. Yet to claim they are beyond criticism because they can keep people alive is absurd.
You could posit this argument about anything we consume. Spinach leaves are to provide energy through photosynthesis for the spinach plant, and technically should not be suitable by consumption by adult humans so to speak if we took your logic to the limit. The fact that we have experienced gain of function mutations that allow us to digest spinach and recieve some nutrient benefit from it mean that we are able to take advantage of this resource. Milk in this sense is no different, even if not all of the human population has recieved this gain of function mutation of lactase persistance.
In biology there is no 'suitable' or not especially in the human sense of things being properly defined into discrete categories of expected outcomes, only what is physically posible through thermodynamics. If you physically can extract energy from plants, meat, milk, dirt, whatever, then its all suitable for consumption. having an enzyme to digest this sugar is no different than having teeth fit to grind down fibrous plant matter, or teeth strong and sharp enough to cut through cartilage and sinew.