What is rationality and irrationality?

Rationality and irrationality are properties of how conflicting opinions are treated, not of specific views. (Except when the opinion is about what to do about conflicting opinions.) For example, a belief in UFOs is not in itself irrational, but the ways in which UFO-believers typically react to evidence is. If the UFO belief wasn't backed up by irrational ways of thinking about rival ideas and criticism then it wouldn't survive for long. Similarly, cannibalism is neither rational nor irrational, except that eating someone prevents his opinions from participating in the debate.