To me, if you believe (i.e. the external phenomenon cannot be observed independently) and it's therefore noumenal / esoteric, then it conforms to an internal logic unique to the individual which in turn depends on the premise/s one creates.

As it's almost impossible to describe these premises entirely with words (because everyone's internal definition of the symbols of experiences differ) discussion can only be limited.

What's irrational to me is when someone's response arises from something they don't understand about themselves - they haven't had time to set up premises to support/create their internal logic. Could be argued that there's a cause for their reaction somewhere but if it exists outside their understanding that would seem to count as irrational.

I don't think that rationality and spirituality are mutually exclusive. We can't really know.