Can you tell me what you suggest if most humans are lactose intolerant then why are dairy products so common?

Milk has benefits...: Here's a benefit you don't always hear regarding MILK: The calcium in dairy products may neutralize potential carcinogens, particularly those found in processed meats. Not all studies agree that milk lowers cancer risk. But recent reports do show that milk drinkers are less likely to become obese. And there is evidence that maintaining a healthy weight protects against cancer.

Lactose intolerance: The percent of the population who develop lactose intolerance you are descended from European populations is less than 10%. It varies depending on your ancestry. It is nowhere near most of the population. If you develop lactose intolerance, the simplest solution is just to avoid dairy. Hope that helps.