I'm sorry but...
Watched about 5 minutes of the first video and I seriously doubt I'll watch any further.
Let's use some common sense, ok? An alien race that is capable of interstellar or even intergalactic travel would be far more advanced than us. Do you really think they'd leave it up to chance whether or not they let humanity know of their existence and presence here?
If they'd want us to know about them, we'd know. If they didn't, we wouldn't. You really think they'd trust the US government (or any government for that matter) with this cover-up? Considering how bad governments are at covering **** up, I seriously doubt it.
If you argue that these aliens are just indifferent to what humans think and that governments around the world are simply doing an amazing job at keeping this under wraps, then I'm gonna suggest you're crazy.
Also, why are people so arrogant and think that aliens would even want to visit us? A civilization that has the capability to travel between stars and/or galaxies surely wouldn't have anything to gain by interacting with primitive creatures like ourselves. Humans are notoriously violent, destructive and greedy creatures, I doubt aliens looking at as from afar would want to have anything to do with us.
But by all means, believe if you want. Tho in my eyes you might as well believe in god, Santa and the tooth fairy as well.
PS! I'm not saying I don't believe extra terrestrial life exists in our universe, quite the contrary. But much like I don't believe in god, I don't believe in other things that just don't make sense and can't be irrefutably proven. Namely that these ET's have contacted us.