Whether Earth was deliberately terraformed, in other words, or whether it was seeded with the spores of life from crashed comets or whether, indeed, life arose here spontaneously and accidentally, it is reasonable to hope that we might find traces of the same kind of process on Mars.
It's odd that invoking the possibility of alien influences should itself be a sign of madness. I don't see the need for it to explain history on earth, but I can't see any reason why the universe shouldn't be full of life.