Unless one believes in a God who made this HUGE effing Universe just for little old us lot, then presumably there must be other smart life out there. If it happened here I just can't see why it wouldn't have happened elsewhere too.

As to whether "they" have ever been here, I simply wouldn't know having never had dealings with ET's myself, but the fact that so many people DO seem to believe that "they" have been here, and claim personal experience of such encounters, is enough for me to assume that such people might possibly be right.

Simply put, I wouldn't presume myself sufficiently equipped to judge the 'true' nature of another person's experiences.