If cats are lactose-intolerant, how did we come to the belief that giving cats milk = good?

Cats are carnivores, meaning they depend entirely on meat and fat for sustenance. We add non-meat products to their food, such as grain/corn, but with enough protein and fat to nourish them properly, as well as a special chemical called "taurine," which is vital to a lot of different functions in the body. Cats cannot digest the sugar (lactose), but they go bananas over the fat. They enjoy the milk for the fat alone, but a cat doesn't know what "lactose intolerance" is. This then gives them the squirty poops, as it does with some people. Most people can see is that the cat loves it, so give it more. We do the same thing with our human children and candy. Terrible side effects, but they like the taste and cry for it, so give them more!