Now correct me if I am wrong but a passports can tell where you are from, where your passport has been stamped etc. Theoretically, shouldn't be hard to implement a travel ban. Now your story about the Nigerian man that went on a plane and did not infect anyone is somewhat of a relief and it can be backed up by the lack of infection in Dallas, despite him being there for X amount of days before finally being diagnosed. But we don't know at what stage the infection is the most infectious, really the most scary thing about ebola is the lack of knowledge on it.
I have read a little more on the first healthcare worker that got infected, and according to some sources, they say she touched her mouth after treating the patient with the gloves she were wearing, which really you can't really blame any other person then herself.
I would like to see myself as a helpful person, as I said I travel a lot, and one time a traveler sitting behind me fainted and lost consciousness after vomiting. See if this happened today, I would be very very wary of even stepping close to the victim which shouldn't be the case. Luckily for that person it was just vasovagal syncope which isn't anything harmful.