The American report that implies UFOs exist is surely just conjecture about things that can't be explained or identified for what they really are?
Looking at the whole scenario logically, how is it that we have clear photo's of all sorts of things out in the vastness of space but no-one has ever produced a clear photo of these supposedly alien craft?
Being realistic, if they were truly alien craft from "somewhere out there", what would the occupants live on? If they've come "a long way", they'd need a huge craft to cater for all their needs? OK, so perhaps we're (I'm?) thinking of life as we know it but all living things need to eat (and dispose of "waste") don't they?
Then there's the speed these things are supposed to travel at? If they're in our atmosphere, there must be some sort of disruption (wake turbulence?) and as they travel at "great speed", there's disruption "in front" of the things? How is it that's never detected? Breaking the sound barrier causes a noise so why don't these things cause something similar?
It's all very well claiming that if "aliens" could get here at all, they must have vastly superior technology to ours and have something beyond out comprehension (at the moment) but our atmosphere is the same for them as it is for us.
Then, just why do they want to come here? What for? Do they just want to buzz around our Planet "studying" us? If so, why and why are they hanging around for so long?
There's all sorts of reasons why someone "sees" something that isn't and never was what they believed it to be. The frequent claim is "I know what I saw". My answer to that is "You think you know what you saw, but what you saw wasn't what you think it was".
There's those that believe that Bigfoot, the Loch Ness Monster and the Yeti all exist but again, all there is to "support" those claims are blurry photos, unsupported claims and supposition without thinking that such things need to eat, live, (mate?), have a family and live from day to day.
Some amongst the human race are crackers, once they get an idea in their head, nothing will change it so where do you stand on the subject of unidentified things?
It's life Jim, but not as WE know it.
Live long and prosper.