Earlier quoted context omitted.
That is indeed awesome but I would argue that it also means we would need to undertake a much more thorough search to find out of mars is indeed a dead planet. Once we land a large concentration of biological matter there -- we won't have an opportunity to look again without dealing with massive potential for cross-planetary contamination. Of course, it's a trade off and it's great news if we ever had to undertake a…
is this a real concern? it should be relatively easy to distinguish life on earth from life on mars, should it exist. Especially considering it comes from a completely new path of evolution. Furthermore, a mars station would allow science to be done directly on mars, rather than having payloads of material sent to and from earth.
But this concern is expressed in that series, and it is a real one. The first people we send to Mars will not be visitors. They'll most likely be colonists. They will die there. Once they start to truly colonize (if they survive) we will loose the ability to determine if any microbes we find are Terran or Martian.