Do you want the reasonable arguments, or the stupid ones? There exist both.
The stupid arguments against dairy: Have you ever tried to milk a wild animal? Cows' milk is made for baby cows, not adult humans. Grok didn't drink milk, therefore it must be harmful.
Refutations: I haven't personally tried to milk a wild animal, but I've seen YouTube clips of others doing it. Beef liver isn't made for humans, so I guess we shouldn't eat that, either? We don't know when our ancestors started drinking the milk of other [domesticated or wild] mammals, but the idea that we shouldn't eat anything that wasn't available during the paleolithic era is impractical. Chickens didn't exist during the paleolithic era, either. Neither did most of our other common meats, fruits, or vegetables. In any case, it's not like an evolved adaptation to thriving on milk would be as slow-going as an adaptation to thriving on grains. Human infants have always thrived on milk; it's only a slight evolutionary adjustment to carry lactase into adulthood.
The reasonable arguments against dairy: We don't know exactly when our adult ancestors started consuming dairy, but it likely wasn't much more than 10,000 years ago, so dairy is therefore suspect, and warrants further investigation. Such investigation reveals that conventional, pasteurized dairy is associated with an increased risk of several types of cancer, certain autoimmune disorders, and perhaps other problems. Therefore, conventional, pasteurized dairy appears to be something most people should avoid under most circumstances. Several cultures have thrived on a diet prominently featuring raw, grass-fed dairy; but raw, grass-fed dairy has not been extensively studied in modern clinical trials. Therefore, the jury is still out on it, even for people who tolerate lactose well. If you want to play it safe, avoid even raw dairy until it is vindicated in clinical trials.