My thoughts,
UFO's are really secret government aicraft that WE, humans, have invented, all by ourselves. The US government is testing these craft all over the world and in space, and they're denying the existence of these craft because they want to 'stay ahead' of countries like China and Russia. They're all just like the old F-117 Stealth Fighters, which were seen and thought to be UFO's before the government told everyone they existed in '89, I think. All of the people in charge of these projects are laughing their socks off at all this 'alien UFO crap.' Most of the UFO reports are fake, and convincing pictures are easily produced. Any true sightings are either misconceptions or government aircraft. UFO abductions are completely fake, and those with actual proof have likely been tricked by the government to fuel the UFO craze. All those researchers who said they worked at Area 51 were lying just for attention (which is just what they thought). I saw somewhere that Brazil admitted that UFO's were real, but they were probably paid by the US to say that (all of those south american countries are in an economic slump).
Plus, space travel between stars is IMPOSSIBLE, and i think that at least in this galaxy all of the sentient races are on the same level, because I bet that most of the stars with planets suitable for life were created at relatively the same time. All this UFO stuff is just a coverup to keep our competetors from finding out the truth, and sooner or later the US will declassify everything.