Losing faith doesn't feel like a betrayal; it is in humility, after all, to doubt, to question. But be the one in whom faith is lost, and you will feel its importance, feel how fundamental trust is to distinguishing friend from stranger, tribe-member from non-person.
Our lives are, in part, an effort to fool all those around us without ever being fooled ourselves, among so many others being just as careful. We know this, know we have a number of faces, know that family sees personality that coworkers don't, and knowing this seek out people who can fool us, and fool us about fooling us, for long enough for us to show ourselves to them without having to be careful.
And there's the betrayal. When you put yourself out there, quite self-servingly, you do it on the promise of someone just as weak and fallible as yourself; rest your weight on their bootstraps since you obviously can't just lift your own. This isn't a promise you demand, but rather that same promise we make each other compulsively, irresponsibly, and of necessity: This is me.
And you trust. You trust them to get it, to get You, on the basis of their own story and your own guesswork about them. If you are wrong about them, they will misunderstand, and if you can't admit to being wrong you'll blame them for misjudging you.
Having faith in someone means admitting that you can be wrong about them, means acknowledging the entity beyond the bounds of your imagination and every belief you have about them. Having faith in someone, while being misunderstood by them, means not letting the story you tell become retarded by the feedback you're getting; it means still believing that they can get it when they don't at first, or indeed seemingly ever.
I think this is why the word "faith" is so often used to describe propagating falsehood, for indeed to selectively acknowledge information about the natural world is to use unnatural wealth to purchase ignorance for the sake of comfort; anti-vaxer movements in the third world never seem to reach a critical mass, just sayin'.
And yet to selectively acknowledge the dispositions of people is an interactive experience, quite different from what we typically mean by delusion. When a loved one insults you, you can take this for their honest opinion or for evidence of a bad day, and react appropriately. When a stone falls upon your head, however, there is no person involved whose motivations you may reasonably credit for the event; saying otherwise is what I think of as personalizing the world, conflating the rules Natural Reality(physics, primates) with those of Social Reality(God, people), and then attempting to affect change in the system by expressing humanity rather than expressing force. I think that a more common, if less interesting, consequence of this tendency to misattribution is the human(and arguably long prior) habit of Depersonalizing other humans through outgrouping for the sake of carrying out intertribal conflict, applying force to sentient systems for he sake of reinforcing group identity.
Faith is necessary, you see, not just to practicing empathy but indeed to being receptive to it. Without taking the leap of believing in a person or group, all you can see is their components, humans and their prejudices; it is the psychological, rather than biological, needs of humans that are expressed in the imperatives of our moral systems, because the purpose of those systems is maintaining the health of communities, not individuals.