Well, this thing is long, repetitive, boring, and still unfinished. Enjoy!
It seems as though the "choice" complicit in determining our beliefs is not so much a positive as a negative choice.
We do not actually choose what we believe; our beliefs are only the most consistent available terminations to the foreground of our thinking at a given time. We do not have direct, volitional access to change the content of our beliefs (they are, to use a computer-term, "read-only"). Of course, by "beliefs" I mean earnest beliefs, not statements (which can be lies) or self-deceit.
On self-deceit: Self-deceit seems to be the closest that one comes to changing one's belief by sheer act of the will. However it is still not direct. Recall that I defined beliefs as the most consistent available terminations to the *foreground* of our thinking. What people know and what they believe are not always consistent. Often, knowledges are present, but have either never been made explicit (perhaps they are very subtle, like the truths that Socrates would bring to birth in his interlocutors), or have been "forgotten" - which is not to say that they have disappeared, but they have receded from the foreground of thought. It is possible for us to wilfully forget things, whether they are subtle points or unpleasant facts. These can be pushed into the background of thought where they have no appreciable effect on conscious beliefs. This is done either by neglect of mental attention to those points, or exaggerated mental attention on a peripheral point that, isolated from its ugly cousin, yields a pleasant outcome. But note that self-deception appears always to be a filter. We do not add an untrue thought to our thinking; we let the knowledge of its falshood slide into obscurity.
But back to beliefs. Beliefs are the most consistent available terminations to the foreground of our thinking. They do not rest high above, aloof from throught, but rather make up a substantial portion *of* that thought (though thought is not simply a sequence of beliefs). Beliefs make up the soft boundaries of the thinkable; thus thought itself is not entirely accessible to the will. What part of it is?
To the extent that we have any control over our daily experiences and inputs, it seems that choice enters here. Like the food we eat, the influences that we imbibe can arrive on our doorstep according to circumstance, impulse or strict planning. Of course the extent to which individuals can do this is wildly variable, and socio-economic class is a strong factor--whether one has cable, Internet access, transportation, a public library, liesure, and the education to know what kinds of influences are where, is strictly beyond anyone's control; those who have these things didn't normally earn them or earn the tools necessary to earn them. Don't tell a destitute Guatemalan villager he can be anything he wants to be. Yet even among the wealthy the breadth of this choice is tightly constricted: there is a grave disparity between the conveniently available, little province of viewpoints that satisfies most in a given 1st world country, and an authentic breaking open of the intellect. Of course I don't mean to draw a line and put myself comfortably on the favorable side of it (though that may be a necessary consequence of merely writing about it). But there is a spectrum, and unfortunately it is precisely a part of the "lower end" of the spectrum that those who belong to it imagine themselves to be at the "upper end". The market couldn't function if it couldn't persuade the masses that they are Inspired Independent Intellectual Individuals (and persuade each that he or she is moreso than most).
Yet perhaps this is looking at it the wrong way. Certainly people have unequal access to the breadth of data generated by the human species in its recorded lifetime. But individually each life can be said to be confronted with every possible choice, irrespective of complex or simple circumstances. No civilization is without its quarrels, its traditions, its wisdoms and its foolishnesses. In one shape or another the entire range of meaningful associations is accessible to every person. Acadamia is elitist; but human meaning is absolutely egalitarian. So we must personalize the question: not what are one's influences, but who.
Our chosen associations affect our thought and thus our beliefs. But how, exactly? It is not necessarily true that one's friends are also one's teachers; as mentioned, Pascal may have played dice with the godless, but not with his belief in God. Shared beliefs are but one of the possible bonds of friendship. Yet still nobody is impermeable to undesired influences; we are "porous", and Scripture frequently warns of associating with non-believers.
I mentioned before that self-deception occurs through the neglect of true thoughts (and these not need be religious thoughts; we deceive ourselves about the simplest and most mundane things). The mind is a bit like quicksand; left alone, objects will sink beneath the surface and disappear. Of course they are still there, but you wouldn't know it simply by looking.
How long can a person sustain the presence of true thoughts in the foreground of the mind? Alone, it would depend on his or her discipline and fervor for truth; yet even religious hermits depend on periodic gatherings and reminders of the brilliant yet subtle nature of their call. How much more necessary, then, would good associations be for those who also maintained associations indifferent to truth?
Again, I make a clear distinction: the danger is not that truth-indifferent associations would put dangerous or untrue thoughts in one's mind (it is scarcely possible today to avoid exposure to untrue thoughts; intellectual provincialism I do not believe is the friend of Christian communities anymore, if it in fact ever was). It is rather that, analagous to the self-deceiver who exaggerates a peripheral thought to forget the deeper thought, truth-indifferent associations exaggerate the presence of peripheral and ephemeral ideas, of zeitgeists, and true thoughts can recede into the background of the mind if they are not brought forward again by good associations.
In short (too late!), it is not the associations that one has, but the associations that one lacks, that have the most profound effect on one's ability to have a breadth of views and truths always in the foreground of thought. The "choice" which is most relevant is not the choice for this or that association but the choice against.
OK, the next installation of this thing should finish it off. I know this essay is kind of weak; but I hope profound insights are forthcoming!