When we think certain states of mind superior to others, is it ever because of what we know concerning their organic antecedents? No! it is always for two entirely different reasons. It is either because we take an immediate delight in them; or else it is because we believe them to bring us good consequential fruits for life. When we speak disparagingly of 'feverish fancies,' surely the fever-process as such is not the ground of our disesteem- for aught we know to the contrary, 103 degrees or 104 degrees Fahrenheit might be a much more favorable temperature for truths to germinate and sprout in, than the more ordinary blood-heat of 97 or 98 degrees. It is either the disagreeableness itself of the fancies, or their inability to bear the criticisms of the convalescent hour. When we praise the thoughts which health brings, health's peculiar chemical metabolisms have nothing to do with determining our judgment. We know in fact almost nothing about these metabolisms. It is the character of inner happiness in the thoughts which stamps them as good, or else their consistency with our other opinions and their serviceability for our needs, which make them pass for true in our esteem.
William James, The Varieties of Religious Experience, Lecture One . Very pragmatist in expression, of course, but the basic point -- that we don't judge whether a type of experience is reasonable or healthy on the basis of its origin but rather on the basis of what we might call its physiology and behavior -- is certainly right.