> I just don't see it. I fully believe that, if there were aliens out there with such capabilities, and they came to earth, they would either conceal themselves fully or reveal themselves intentionally (and not just to a handful of people in a remote area).

After having read Roadside Picnic, I'm inclined to disagree. If sufficiently advanced aliens ever happened upon us they might treat us as we treat ants in our backyards—that is, they don't really notice or care for us at all.