simple. because those persons can go to a third country and then travel from there. it creates an impetus for persons from West Africa to simply try to evade such controls. this would of course worsen the situation, not improve it.
the world as a whole needs to be sending more resources to West Africa to fight the epidemic *there*. that is the only thing that will help stop this from becoming an actual pandemic.
Err...with our flight systems, can we not pretty readily track anyone flying OUT of that area, and know if they are coming from a connecting flight within the 20 or so day incubation period?
I have nothing wrong with sending resources...BUT, I still see no reason to allow free travel out of the area especially with cases on the rise, I hear projections that soon it will ramp up to 10K a week or so over there. At some point, we need to expand the quarantine to the NATION and not just hospital rooms.
Better than have it reach pandemic proportions, and we "rest of the world" find ourselves in a position of deciding to do something even more drastic. Better to close the area off till it can be controlled, than to have it become Uncontrollable, and we have to resort to measures to protect the world by "cleansing" the area in a much broader sense. (warms up the nukes).