This is ridiculous. Any civilization that has the ability to study us at either a distance or up close indicates such a quantum leap above us in engineering and raw wealth that they would register as at least a Type I on the Kadashev scale. A Type I civilization has the technology to enable de facto immortality, stellar level engineering (Dyson Spheres, Von Neumann probes, and other fantastic works), and would likely have a military contingency to deal with aggressive upstart civilizations. If they were so morally superior (what the hell is this, Star Trek? Do we all have to be spandex wearing buttfucking pacifists to be moral?) they would brew up a bio weapon, seed our atmosphere with it, and swing by once we're all dead.