EP, what you are implying would then also pertain to any other planet/planetisimal capable of sustaining life outside Earth.
Precautions were taken when the Moon was studied. I'm sure they will take the best precautions available when they study Mars.
Who knows, they may find a cure for AIDS(and then some) out there.
Yes, by all means, send robotics to do the basic research first, but not to attempt to do ANY study at all out of fear... (?!!).
Marcia