If there is life, then I believe we should do nothing to disturb that life. Mars then, belongs to the Martians, even if they are microbes.
Whatever the reason you're on Mars, I'm glad you're there, and I wish I was with you.
A blade of grass is a commonplace on Earth; it would be a miracle on Mars. Our descendants on Mars will know the value of a patch of green. And if a blade of grass is priceless, what is the value of a human being?
In our time, we have sifted the sands of Mars, we have established a presence there, we have fulfilled a century of dreams!