If we did it for Israel, why wouldn't we have the authority to do it for Liberia? Don't we have the authority to issue directives to our own airlines, and permit who and who does not have permission to land in the U.S.? For example, if Cuba wanted to send a commercial airliner to the U.S. without our permission, could they do so? I guess I don't know who rules the skies, in general, but I thought we had jurisdiction over our own airports.
Maybe as a compromise we could route all West African air traffic to a specific U.S. airport specially designed to handle the situation, and to process passengers more thoroughly than a standard U.S. airport.
I have no idea how many negative effects it would have on the economy to stop all air traffic to/from Liberia coming to the U.S. for (arbitrarily) six months, but I can well imagine the negative effects if ebola starts getting out of hand in this country.
If Liberians with ebola and U.S. passports see that a quick flight to the U.S. results in immediate treatment far better than what they can expect in Africa, and at no charge, you could hardly blame them for doing everything they could to get here in that circumstance.
Just something to think about!