We evolved to do it recently, but lactose tolerance genes have been heavily selected for by evolution. It's one of the most heavily selected-for traits in the past ten thousand years.
Still the majority of the world population is lactose intolerant and should not be consuming dairy at all.
The ones that can digest it, do it usually less well than they think they do. Mild chronic diarrhea is prevalent is western countries, and a degree of dairy intolerance could very well be one of the factors.
It gets worse for most people with age, as elderly people can become lactose intolerant, fully or only slightly. This does not happen overnight, its a progressive thing, many people gradually stop being able to properly digest dairy.
There are different degrees of lactose tolerance, and a good fraction of the world's population is at least somewhat tolerant. Then there are regions of the world where almost all people are completely tolerant, like northern Europe.
There are also lots of dairy products that contain little lactose, from lactose-free milk to cheese. And of course, it's pretty simple to just take lactase pills.
From a completely subjective perspective, dairy products are some of the tastiest foods, and they're objectively a huge part of food culture in Europe. I don't foresee them going away.
