How can a church keep people from choosing what they want?
Very easy and goes on all the time, in some way or another. You see, it's not "choosing what they want", rather "defining what they think they want". Do not underestimate the power of the pulpit in an organized religion.
In Malta, where the Catholic church has a very strong presence (in fact Catholicism is enshrined in the Constitution as the "religion of the Republic of Malta"), the Church is taking every opportunity to make its position known on an upcoming referendum on divorce - fair enough, as far as that goes, but one high-ranking prelate even came out as saying that voting in favour will be a mortal sin. To be fair, he was quickly shushed by the Church authorities, but one feels that this was more because of the predictable reaction from the more liberal media than any disagreement with the principle.
And going back a bit further in our history, in the sixties the Church twice issued interdicts on people who dared vote for leftist parties (
http://en.wikipedia.org/wiki/Interdict) - and the leftist parties lost on both occasions. It may have been a good thing for us at the time, since the Labour Party at that time was quite extreme with Communist tendencies, but the action was reprehensible and certainly divided the people, a division whose effects we are still feeling forty years on.