Which has caused more human deaths in the last 25 years: all livestock-borne diseases combined, or diseases which are spread human-to-human via intimate or blood contact? It used to be that humans with certain diseases were required to be quarantined. If one's concern is with controlling disease, does it make more sense to put in an unprecedented program to track countless millions of animals, or to follow precedent in tracking and quarantining a much smaller number of diseased people?
I assume yours was a rhetorical question?