Couple of things, and I might have said before.
The word "alien" does not appear in UFO. I'm sure the Government loves people making that assumption and driving themselves crazy.
"Voices" at Skinwalker Ranch, and in other such stories, used to sound batshit crazy until I learned there's a frequency that can literally broadcast sound directly to your brain so you can hear it from inside your head. It's literally the perfect weapon because noone believes you're sane when you describe it.
Back to aliens. Maybe the people in charge really are that stupid, but it seems to me if any Government had actual proof or contact with an alien race advanced enough to get here, there are only two logical choices: destroy every other culture to endure only we get to deal with them, or make it public to unite the world in case they're hostile since that's the only chance we would have; united so they don't have to choose the "better" civilization or united in combat.