Conspiracy is a curious word. It comes from " conspirare" which means breathing together.
So, let's consider for a moment that the idea of Extraterrestrials coming to our planet is true.
However, if this is so, and if the government is in contact with the Aliens, then both, the authorities and the ETs are co-conspirators. Both are involved in a huge conspiracy.
Consequently, to point the Government as responsible for the so called Cover-up is limited to one of the parts. Obviously both, ETs and Gov. are keeping the Cover Up, the secret of the extraterrestrial presence on our Earth.
If this is so, the aliens conspire against Humanity. They are allied with the government. They are hostile to us, the people.
Gov and Aliens breath together. Conspire against us.
Obviously, the disclosure would be the recognition of the Aliens-Government conspiracy.
The whole thing is contradictory, illogical and irrational.
More, it would be impossible to keep such Cover-Up.
The conclusion is that Extraterrestrial massive presence implies contact, open contact. Since this open contact doesn't exist, there are no Extraterrestrials here.
The UFO phenomenon however is here from the beginning of times, but the ET hypothesis doesn't solve the enigma.
From our perspective, after decades of research, the Time-travelers hypothesis is more rational and explains the lack of contact and the furtiveness of the Entities behind the phenomenon. Time-travelers cannot and will not destroy time continuum.
The ufonauts apparently work in a different space-time dimension, but again, if this is so, we cannot understand how they do it.
So, the whole phenomenon remains a mystery. An unsolved mystery.