Years ago there was quite a lot of discussion on overpopulation. That topic is not even brought up now days. I have no explanation for that avoidance.
The high concentration of people is how these virus outbreaks spread so fast and far before it can be isolated. Especially with air travel moving people all over the world constantly. Just like deer overpopulating an area and disease sweeps through the herd and knocks the population back.
If a serious and lethal pandemic were to hit in a big way the cities would be the most vulnerable. If these cities were quarantined it would be near impossible to survive inside the quarantine. Even separation outside high population centers would be difficult due to the need for necessities and family movements, but obviously a much better survival rate.
Any high concentration of critters or humans is ripe for thinning.