Everything is fine if reality and expectations are in line. But many societies are projecting economic growth at levels that have historically been underpinned by the increase in demand from sheer population growth, as well as the increase in supply of labor.

Edit: The other issue is tribal. The global tribe has lots of sufficient labor and young people to offset decreasing numbers of young South Koreans, but humans are not fungible. There will be many types of conflict due to cultural differences, as well as shifting power dynamics and the resulting lack of acceptance of newcomers on the same level as native tribe members, etc.