Faith is not only necessary but contagious. We want to believe because we want to be cared for/valued. Belief is infectious because it is tiedto our need for love. We are drawn to love like a moth is to flame/light.
This is why we are so easily allured to promises that can (or may) not truly deliver. Though we like to think our views are based on reality, they are based more on belief and hope then irrefutable facts.
However we are only quick to trust and depend on anything and everything except God. Why? What God offers is often not immediate but a long term solution. What we want however is immediate resolution or relief. Long-term relief requires greater trust and patience and is outside our control (eating a treat or watching a movie on the other hand [or whatever is our "drug" of choice] is more immediate and more within our control).
This is also why people are so emotional/passionate (even volatile at times) about their views (e.g. religion and politics); they are tied to their need for love, a sense of well-being, purpose and meaning. If you mess with my beliefs you are messing with me, my identity and my sense of value i.e. our belief system is more emotionally than intellectually based.
This is also key to how you change someone's mind. If you wish to win someone to your way of viewing things, you treat them with more value (love) then their current belief system offers or provides. Love (meaning/purpose/value) after all is what we are really after.
Trust and "gathering facts"
The reason we must trust is we are limited in the facts we can gather i.e. we are finite. We don't know everything and can not be everywhere to observe all that is "out there" to observe. Much of our views are based on what we don't know but simply must believe is so (we know what we know, but it's what we don't know that is our challenge). This is why someone's commitment to a particular view may seem irrational to others who don't hold that view while perfectly rational to those that do.
For example, I don't see God, therefore I don't believe he exists. And since he doesn't I am not accountable to a Creator and free to choose how I conduct my life
I believe there is a God because I see design, beauty and love in and around me indicating there is some kind of meaning and purpose to life. Purpose suggests a higher will (or Being) then my own.
Neither of these views can be proven in the absolute sense due to our finiteness, so we interpret them to mean what we choose to believe.
In summary, we can not operate without faith, no matter what our world view. And since we are designed for love we gravitate to that which meet's that need best from our limited perspective. Faith is not only necessary because of our limits it is necessary in that it is tied to our very sense and need for value/love. Because of these two factors faith is not just unavoidable, it is contagious.
For a further discussion on being finite click here.
For a further discussion on being designed for love click here for several related articles.