The thing is, an awful lot of people do believe in aliens, even in different varieties of aliens with different agendas, and a surprising number of people believe they've experienced manifestations of aliens or alien technology. I went to a small birthday party recently and to my surprise almost everyone there acted as if the activity of aliens among us was common knowledge, and several acted as if they knew them personally.
But they seemed so normal.
I don't see why this should all be dismissed as fruitloopery.
There is a very good book called The New Inquisition, which in the end is mainly an observation about human psychology and human knowledge, based on detailed analysis of experts' reactions to startling new theories.
It does seem that as a species, we have a tendency to intellectual conceit, and to believing that we know everything. For almost every new discovery that humans have made there have been known experts who have scoffed and discredited the new idea or technology. Sometimes they have been proved wrong, sometimes, the ideas have never even been properly tested as with Tesla's world grid. But bear in mind, when Tesla invented AC electricity, the experts all scoffed and said it would never be possible for such a system to be the main electricity provider on large national grids. Sometimes, when the mainstream worldview has enough power, they suppress the new information by throwing the author into prison, and burning his books, as with Wilhelm Reich in the US in the 1950's.
http://skepdic.com/orgone.html,
http://www.orgone.org/wrbiog/biog00.htm
But the basic point is, when a single-vision worldview is threatened, (i.e. a world view that knows what it is, and knows that it is right, and all the others are wrong,) the holders of that worldview react in peculiar ways.
Personally I'm sure it's impossible to find out the "truth" of 9/11. But I wonder, if in fact, for example, the reality was that the planes actually materialised out of thin air, then what explanation would we have had presented to us.
Could any existing government agency seriously have investigated 9/11 and come out and say " Ok, folks, we've investigated it, and the conclusion is, the planes materialised out of nowhere." It would be just incredible, what kind of a world would we then be living in?
Sure your worldview may ensure that you know that you live in a predictable sort of world, where impossible things like that don't happen. But there's an awful lot of human experience to the contrary. So myself, in the circumstances, where I know I don't know everything, I prefer to keep an open mind. I think it's fair to call that rationality. But I'm sure you all know this anyway.