If a person is convinced our government is in cooperation with Aliens, the sky is the limit on what else can fit that narrative. This position makes it much easier to believe any action needed downstream from that same government.
If I don't happen to believe the Aliens-Government thing at all as we both know. This makes me less likely to believe the government knows about Bigfoot and is keeping it quiet.
I can agree our government would do some of the things you might imagine involving areas of National Security. Again, the Magnitude is the defining issue.
The funny thing is I am more than willing from my perspective to open the door to your position provided I was given a good enough reason the issue raising to a level like national security. (There is that darn Magnitude again).
Once someone is convinced of the Close Encounters world, anything they dream up is always possible. Such a foundational belief makes your type of conclusions much easier to believe.
Since I am convinced our government WOULD do a massive UFO cover up should they exist, I just happen to require any other issue rises to that level.
It is all about the magnitude, as it should be. It's not "silly" at all.
I respect where you are coming from. I don't know how else to say it but I don't buy the first thing (Government-Alien-Connection) so I can't buy the second thing (Government coving up Bigfoot). If one buys the first thing then they have the mental currency to buy just about anything.
I have found sometimes discussing these things with those convinced came come across as an attack on what they happen to believe. This isn't the case. It's just a respectful disagreement.