If I were to venture a guess as to why the government puts so much effort into debunking concepts like aliens and time travel, I would suggest that they have something to hide. Why would they care unless they are protecting something?
Take the government sponsored heliocentric model of the universe (a spherical Earth revolving around the sun). Up until the 1400's people believed in a geocentric model (the sun revolving around a flat Earth). Historical texts, including the Bible, show that this is how the population viewed the universe. Suddenly, in the 1400's, the heliocentric model was introduced, which quickly got the approval of not only governments, but the Church as well. Despite the evidence against a heliocentric model, all kinds of money was thrown at scientific grants, education, and the mass media to support this theory. Yet, we were not able to get up high enough to look down and check until the 1960's. I think it is much more plausible that once we got up there and learned the truth, the government decided it was much easier to lie than to admit that it was a stupid idea to put a globe in every classroom.
As for your experiences with aliens, I think there is entirely too much evidence available for a rational person to dispute their existence. Those that do are either part of the cover up or are too fragile to accept that their personal views might be wrong. My main question is exactly where they come from. While Hollywood would have us believe that aliens come from outer space, I consider it more feasible that they would be from the future, other dimensions, or underground.