"It's life, Jim, but not as we know it." Who says the alien has to breathe oxygen? Who says it must be bipedal? Who says it has to be physically tangible?!
Ugh, as for colonizing the moon, I fear that people will also want to mine the moon (poor Luna!) as well. Yeah, yeah...about that, let's look at every other post-apocalyptic science fiction. First, what happened to the moon? It asploded. Second, why did this happen? We mined it!!
I wouldn't care if the scientific community proved that there would be no repercussions from the mining, I'd still be against it on the grounds that nobody owns the moon, and that we don't even have the right to reap it of it's resources.
About the further colonization efforts by mankind, I'd rather see us floating through space in huge vessels than see a planet be terraformed, though if we happen to find a habitable planet that has no sentient life, or that's on it way to becoming sentient in a few hundred years (not sure how we'd determine this), then okay, let's set up shop.