In a purely practical sense, we need to do this so we know exactly what the health status is for these people who come to our country. We need to know if they are healthy or sick & if sick, sick with what. Ignorance is not bliss in this case. If we can cure it then we will be healthier too in the end because it won't be spread here. It is possible to do things with more than one motivation. Humanitarian needs & self preservation can both be served here.