Heh! Excellent example, Amos. People always seem to figure they already basically know about all the stuff that's worth knowing about, and the rest is sheer nonsense. It's the standard reaction to unusual possibilities or unexpected information.

Maybe they are already here, Bun, but keeping a rather low profile. I would do so if I was them, because Earthlings are extremely dangerous at this point in our social development. I would take a quick look, and get the hell out. Perhaps they are merely observing us (as we might observe a colony of unusual but very dangerous animals), and waiting for us to move beyond the social stage of being violent, aggressive adolescents who spend a sizeable chunk of their material and financial inheritance every year planning on how best to commit mass murder upon each other.