Lactose intolerance is the norm for humans. Somehow this doesn't get communicated since practically no one knows it. Up until somewhat recently all humans were lactose intolerant. Iirc tolerance started with starving Europeans making full use of cows a few thousand years ago, then over time people became able to tolerate it.
Experts estimate that about 68 percent of the world’s population has lactose malabsorption.
Source: https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/definition-facts
All that to say yeah, it's a very common condition and most people who have it probably still eat lactose as it's not all that bad to get the shits. Come on, it's cheese and ice cream we're talking about here. And pizza. Even if the consequences were awful, humans are also pretty good at ignoring consequences when deciding if they want something they really like