Rationality can have everything and nothing to do with faith. It's about following things through, so it depends on your starting assumptions.
http://en.wikipedia.org/wiki/Rationality
Atheism, for example, is not a rational viewpoint unless you accept the concept of logical positivism to be totally accurate, and science as a means that would provide clear evidence if a diety existed. You basically need to have faith that science would provide the evidence, should the idea be true, and therefore absence of evidence is the same thing as evidence of absence.
If I have an unopenable box, what is the rational position to take on the contents of it? Full, empty or unknown? We have no evidence the box contains anything, but can we say that absence of evidence is evidence of absence?