Yes, I think so too, and all the ancient wonders (that are the structures) of the world are yet to be puzzled out as to how they could be built.  All of them are beyond what engineers can build in this day and age.

As far as them being here now, I think it pays to have an open mind. We certainly don't know everything, and there are plenty of people out there who have a lot of stories of their encounters with aliens.

I think the main resistance to even considering the possibility of e.ts, is fear.  Because if they're bad and have a malevolent intentions towards us, there's not a whole lot we can do about. On the other hand if they are good and want only to help us evolve then that would also higher fear with our mainstream religions and social/economic/government systems. Worldwide panic is not an easy thing to deal with.

I don't have the details at my fingertips but will get back with details, but there is a story that,   Eisenhower and the De Gaulle, Churchill and other world leaders supposedly met with Extraterrestrials in the late 40s and early 50s, (after Roswell in 47).  And it was decided the general public could not handle this information because the for mentioned reasons.

But there was some kind of understanding or pact among the world leaders and E.Ts. to keep silent for then.
 So possibly there are Aliens on our side too. Or that they take great  interest in us. More on this later.