First, let us consider the different kinds of possible Cover-ups.
1) The first model of cover-up is just the denial that those UFOs that resist any conventional explanation, are the evidence of some kind of advanced, non-human technology. The gov. doesn't want to recognize that the UFO Phenomenon cannot be stopped. The gov. would be forced to recognize his own VULNERABILITY.
2) The second model of cover-up is based on the idea that the gov, KNOWS who the Aliens are, and perhaps what they want. They will not recognize this knowledge.
3) The third cover-up model would be the complicity of the gov. with the Aliens, and includes some kind of hypothetic contact with the unwanted guests.
4) The fourth model suggests that the government is controlled by Aliens. The authorities perhaps even have knowledge of some Alien technology. We are then colonized by one or several Alien races.
Where is the paradox?
The Exos rhetoric always choose the last two models of Cover-up: Why?
Just because the biggest cover-up will justify their paranoid rhetoric. The EXOS can tell us what they want, and any demand of Evidences will be denounced as disinformation, debunking, and provocation.
The neo-cultists will protect their total lack of evidences in the shadow of an omnipotent cover-up. The paradox is that the Exos are protected by the same cover-up they denounce.
Ergo, is possible to suggest that the EXOS are part of the cover-up. Their unsubstantiated claimings makes the UFO Phenomenon look ridiculous and keep the good, rational minds out of the inquiry.
--
entia non sunt multiplicanda praeter necessitatem,
"Occam's Razor"