Which causes what, though? You can condition pretty mich any body to be able digest milk just fine. Unless you are actually highly allergic to it, maybe. It‘s easier when you‘ve had milk growing up and never stopped but people who have stopped sometimes lost the ability to digest it properly. On the other hand there are former lactose intolerant people who brute forced milk consumption and after weeks of diarrhea adapted to it as if they never had anything else in their life. I think it‘s far less about generics than many people think.

Regardless, milk consumption has the nasty side effect of being terrible for the environment. CO2 emissions from milk products are insane.