You've never heard of religious conversions? Or people losing their faith?

I think it is easier to change our beliefs about some things than others, but that has more to with how that belief relates to our other beliefs. If a particular belief is not just something we believe to be true, but is also a framework we use to make sense of the world, then new information is rarely sufficient to contradict it. With any worldview/religion/ideology, you're going to run into facts that are difficult to explain in light of it.

> You've never heard of religious conversions? Or people losing their faith?

Are these conscious though? I always assumed faith was spontaneous. You don't just read a holy book and become a believer right? Faith stems from one's upbringing and/or deeply felt religious experiences. Whereas a non-religious book that gave you new facts about a particular topic could potentially convince you to change your mind.

I think you're right that opinions are harder to change the more fundamental to one's worldview they are.

I see the change in belief as always being a two-step process:

1. Receiving and understanding new information

2. Processing and integrating that new information.

When the belief you are updating is a relatively unconnected node in the graph of beliefs, that second processing step takes almost no time. If it's heavily connected, the processing takes longer. That's why conversions often seem "spontaneous": your subconscious has been busily reworking the web of beliefs to integrate the new information, and eventually everything clicks into place and you have an epiphany.

I don't see faith as some special category of per se. To my mind, faith is simply another word for trust. The implication is simply that it is a belief you are willing to act on.