If we don’t shut down flights, we will be encouraging people to make a run for the US if they think they are sick.
Get to the US and guarantee the best possible care. It will be a problem.
...and no one is saying there would not be a process to evacuate American citizens from affected regions. Send a hospital ship down there, quarantine citizens until they are clear of disease, then let them come home.
LIberians, non-US citizens? No.
Plus, if you think about it, those arriving in America will be getting free medical care. How many of them have health insurance? How many of them will be able to pay the hefty hospital bills resulting from their treatment if they come to America for that purpose???