I don't think the care as much about contamination in the way it might mess with the martian ecosystem, what they do care about is getting uncontaminated results.
Finding a life outside of Earth will be one of the greatest discoveries of man kind, something that will never be overshadowed by anything. They want to make sure that when we'll find something it didn't catch a ride on what ever we sent to find it.
Eventually when we start exploring space it wouldn't really matter, yes some precautions might still be kept but we wouldn't take as much care as we do now.
I for one also do not see humans contaminating an alien ecosystem as something unnatural, humans evolved, they've spread out, they seed life (intentionally or otherwise) this is just as much of a natural process as the potential for comets and meteorites to seed solar systems and beyond with organic compounds and even life it self.
Finding a life outside of Earth will be one of the greatest discoveries of man kind, something that will never be overshadowed by anything. They want to make sure that when we'll find something it didn't catch a ride on what ever we sent to find it.
Eventually when we start exploring space it wouldn't really matter, yes some precautions might still be kept but we wouldn't take as much care as we do now.
I for one also do not see humans contaminating an alien ecosystem as something unnatural, humans evolved, they've spread out, they seed life (intentionally or otherwise) this is just as much of a natural process as the potential for comets and meteorites to seed solar systems and beyond with organic compounds and even life it self.