Does the US Government keep secrets about Aliens?
Anybody who thinks intelligent aliens are visiting Earth does not understand the distances involved in interstellar travel, or how primitive and uninteresting humanity would be to any race capable of achieving it.
The people who believe this kind of stuff are crazy. You ask them for evidence and they tell you they can't give you any because the government has destroyed it.
Which kind of begs the question of how they know about it in the first place.