The survived miners will probably have children. The children who are not fit (neither physically nor mentally) will die working in mines. The mentally fit children will migrate to US. The physically fit children will have more children that are physically fit. What will happen then? Why are we ignoring the future of our species and human rights on a larger scale of time?
There are also studies about generational poverty, medical literature on helping people recover from traumatic conditions, etc..
Not to read any bad intent in your comment, but there also have been studies about social darwinism that have a long track record of problems. I think people do still do studies about genetic inheritance etc., but it's probably impossible to draw society-level conclusions without data.
Because we like money.
Outside of a few wealthy democratic enclaves, the world is largely a place where the rule of law means the rule of the strongest, where human rights don't exist, and where everything and everyone can be bought for the right price. This includes international waters.
I think he is just wondering why we don't consider the impact of immigration on genetic diversity. If we have nations that have huge immigrant populations and nations that have huge numbers migrating away from them it would have an interesting impact on genetic diversity. There are a range of traits that influence whether someone would migrate from a place or stay where they were born. I don't think pondering the effects of that requires a psychiatrist.
Note that even in more enlightened places, the ultimate tool for enforcement and coercion is still strength, and the state has a monopoly on the use of this.