probably a lot of not asking the right questions out of shared guilt of our species and today's dominant cultures and perspectives. (the whole conquest is heroic instead of the robbing others of their development and earned cultural wisdom that it is. some rogues may be out their to concor, just like our own, but what if the majority are concerned with protecting each other from being invaded, like some kind of galactic united nations. to whom our idea that the univese was created for us, must be at least alarming, and while we are little or no threat now, our potential to become one of the rogues, instead of a good and considerate galactic citizen, is at least a legitimate concern.) the real question is not how many and which of them may be "friendly" or "hostile", but weather our behavior toward them is to be rational and responsible. (not something our dominant cultures have a history of being very good at)
I have just watched a documentary of which suggested the stealth bomber was inspired by back engineering alien technology. Many of these documentaries also suggest that the US government made the following deal with aliens. The US government is said to have received advanced weapon technology for turning a blind eye on alien abduction.
Revealed: Why We Should Look For Ancient Alien Spacecraft On The Moon, Mars And Mercury According To NASA Scientists
Will Lunar and Martian archaeology reveal ancient civilisations? Will they find the remains of humanoids that were able to fly in the anti gravity with real wings? What will it tell us about our own ancient history?