Life On Mars

When we search amongst the stars, why is it that we're always searching either for new physics, or for life? Why do we suppose that the most interesting phenomenon out there must be something familiar to us on Earth?

And if the most interesting thing "out there" is life, why do we keep destroying the life we do have at home on Earth, even as we know that we haven't even begun to scratch the surface of exploring this thronging hullabaloo?