Hot Zone
was a popular book on the many dangerous viruses in Africa, etc. which could wreak havoc on industrialized societies. The thesis was that we are siting on a time bomb of dangerous viruses, like the still unknown variety of flu virus that killed more people around WWI than the war did. The upside to microbiology from the study of another planet's life forms would be huge. We have only 1 sample of life to study here. Is Mars life (assuming any) DNA based or not? Implications either way are paradigm shattering.