It has been proposed here that a belief is only respectable as long as it's backed up by evidence; at the same time, it has been proposed that a belief is respectable in the exact measure that it benefits mankind.
Let's then imagine that a rationalist meets an evangelical Christian whose faith in Jesus moved him to start a hospital for the poorest among the poor in a third-world country. How is the rationalist to approach the faith thinking of that Christian?
On one hand, we have a faith-thinking that does not adhere to reality: The evangelical Christian cannot provide solid evidence for the inspiration of the Bible; that the Jesus as portrayed in the Gospels ever existed or even said what he is purported to have said; he cannot reconcile without contradiction his belief in a God of love and the existence of evil in the world; he is blind to the contradictions of the Scriptures and discards all Bible accounts where God is shown to act with cruelty or condone violence. All he believes (even against evidence on the contrary) is that Jesus taught that his followers should help their fellow human being; and such good will someday grant those believers access to everlasting life in heaven.
And yet, on the other hand, it is this same irrational faith (irrational because isn't backed up by evidence) that motivates him to do something that unquestionably is a worthy service to mankind. How, then should one approach such belief? What matters most? That his beliefs aren't adhering to reality and cannot be backed up by any form of evidence? Or the fact that his beliefs drive him to pay a service to mankind?