Yes and no.
First off, each country only has so many international airports or seaports. A person suffering from a viral hemorrhagic fever such as Ebola or Marburg would be showing some ridiculously painful symptoms. This would alert the crew, who would then contact the host country they are flying to as to what they should do. The host country, or at least the country in question, would then direct them to a particular place where they have HAZMAT teams ready to deal with this kind of issue. Many westernized nations have the capabilities to deal with this kind of issue.
Secondly, while Ebola is certainly virulent, and can be transmitted easily throughout the human population, you need to remember that Ebola is transferred through physical touch. It is not airborne, otherwise the kill counts would be much greater. Furthermore, it is perhaps a grim silver lining that Ebola kills much too quickly for it to spread very easily. These two aforementioned reasons are why the death counts in the afflicted African countries is not higher.
Thirdly, I'm not quite sure how several impoverished (by any stretch of the imagination) nations are going to "fight back" against any developed country, let alone a hypothetical WHO declaration of quarantine against a certain nation, backed by the full power of the UN and its peacekeepers.
I feel like, while the situation is obviously dire, everyone is freaking out a little bit too much about this.