See - if he was not allowed to return to the US, then we would have nothing to worry about.
Of course, he might have traveled to France then Canada instead, infecting everyone he came into contact along the way, and then they might have come here from Canada or France, but what the hell do we care about real risks when we can sit back fat and happy thinking wqe solved the problem by prohibiting travel from a few countries.
Wasting resources - political, social, or monetary - chasing foolish solutions is the height of foolishness.
That is why an ineffective and inane travel ban on a few countries actually increases our risk of exposure to ebola and decreases our chances of containing it.
Knee jerk solutions usually just result in sore kneees.