If you want to look at it through a historical, economic, and games theory viewpoint, I'll oblige.
Considering that:
1) The UAPs are actually exo-Earth visitors
2) They've been visiting since the 1950s
3) Our government knows and is keeping quiet
That's extremely worrying. Look at history. A well-funded explorer visits a new land, explores, and takes back some interesting stuff to show off. Within a few years more well-funded explorers visit. Not long after that, someone sees a profit to be made if they can get colonists to go. They economize a process to get a bunch of people to move to the new land and settle, then begin commerce.
The natives are concerned, but really like the shiny new baubles the settlers trade with them, so some abide. Others see the threat the settlers bring. They fight and try to eliminate the settlers. The settlers that survive are profitable, although most of the profits go to the profiteers who maintain the lifeline to the homeland. The profiteers see a threat to their profit in the natives who fight back, so they bring in military force for "security".
The natives get f***** from then on out. Your only hope is that the space-faring society that is "visiting" has evolved to understand the destructive nature of imperialism, i.e. Star Trek's "Prime Directive". Don't count on it. An unregulated capitalistic space-faring race will strive to dominate anyone they come in contact with.
The fact that the government is keeping silent is likely a good sign. They're gaming this out and trying to ensure our survival. Naivete would be exemplified by excited, cheering announcements. There is also a chance that leaders have made deals for themselves, but they know history as well and they know that the leaders who caved always got f***** as well.
The other thing people don't consider is relativity. Time in space travel is not a constant. Interstellar is the only sci-fi I've ever seen that tackles this issue realistically. Even if the visitors have faster-than-light or warp travel, the spaces they are moving to do not have equal movement in time.
We're on the outskirts of the galaxy, and we're a bit out of the galactic gravity well. Our time passes more slowly than time passes nearer the center. This is good for us, because it gives us more time to prepare. If the visitors are from closer to the center of the galaxy, they could well be worried that we are advancing faster than them, and although we're behind, we could pass them technologically in a short amount of time. The corollary to this is that if they're already more advanced than us, they probably come from further out of the gravity well of the universe and we're not likely to advance as quickly.
This also affects the visitors in another way. If they come from further out in the galaxy, visiting our planet for a couple hours could mean that by the time they return home everyone else has aged significantly. They're now younger than their peers. If they come from closer in the galaxy, visiting our planet for a couple years could mean that they return home and little time has passed, meaning that they are now older than their peers. It takes time to get their intel back from here, and how much time does that take? How quickly can they respond? Etc, etc.
I can guarantee you the government has paid some very brilliant people to game all this out and formulate a plan. The question is whether or not that plan is already in action.