Many people "know" the aliens are real.
They may or may not have seen anything alien for themselves, but many people can deduce from all the evidence, eyewitnesses and obvious cover-ups that there "must" be something to it all.
But it is at a point beyond this realization that things really start to get confusing, because all kinds of people will believe just about anything "about" the aliens.
They hear a lot of craziness, much of it designed propaganda, so even the truth sounds like more craziness, and they do not recognize another option.
They make a choice of whether to deny any belief (or hope) that there is other life, or to accept something among all that craziness.
They do not fathom the order to the Universe.
They don't realize that even though they hear all the yack yack yacking from so many people making various claims, hardly anybody on Earth knows the aliens at all, not even the people who have experiences with them.