Here is a fact. The very air we breath is most likely fatal to any “alien” out there. So, most likely, if they are “visiting” they are sending drones. After all, arent we sending drones to other planets?
Fact number two. If they have the know how to get here from another galaxy, we wouldnt be here any longer. We’d most likely be either slaves to them or cease to exist unless we are/were lucky and have had “visitors” who are not aggressive.
Fact number three. All government agencies would issue so much false information on the matter that nobody could sort out the facts from fiction.
#1 If they are not from earth or related to earth life, they’d be susceptible to earth pathogens. If not, they would not likely be well acclimated to our conditions. Either way, there are lots of other reasons, strategic and practical, to avoid direct contact. Now we would call them drones. In the past, robots or probes perhaps. It is likely that their sophistication goes far beyond these concepts, including massive realtime AI coordination among dievices or perhaps entities.
#2, You can’t assume that the origin is remote and thus any need to traverse celestial scale distances, let alone the fact that it may not be such a massive leap to achieve that soft of engineering. Barely more than a century ago we were not commonly using air foils to achieve lift.
Also, the concept of ‘aggression’ may not apply to other forms of ‘intelligence’ in the same mammalian pretexts that we use. Just because they haven’t overtly enslaved us or yet destroyed us (humans, all of earth, or some combination) doesn’t mean they can’t arrive at a motivation to do so in the future, or perhaps they are patient and methodical in their assessment and subsequent planning of such.
#3 there usually has to be a significant socio/political motivation for such large scale dis-information or counter-intelligence. What would that be, other than the standard desire to keep things status quo?