Cultures that are self sustaining will exist into the future. If the Korean culture isn't one of them, so be it.
There probably were many cultures like modern Korean throughout history.
And since they collapsed they...well don't exist anymore obviously.
Natural selection.
I'd like the average human in a 100 years to be a bit more like me and a bit less like the average human today. But the rest of the Western world doesn't seem to see it that way.
Are you aware of the research that correlates homosexual traits in men with higher fertility in women from the same genes[1]? These factors are not a strict net-negative. In addition, "culture" isn't transmitted genetically. You could spread a culture with below replacement reproductive rates if the culture was persuasive enough. There's not a "democracy" gene that suddenly emerged and spread from 17th century England. It was the ideas that spread.
[1] https://www.newscientist.com/article/dn6519-survival-of-gene...