Repetition Drives Home a Viewpoint
The headline to the article says it all: People Often Think An Opinion Heard Repeatedly From The Same Person Is Actually A Popular Opinion (via Kottke).
...repeated exposure to one person's viewpoint can have almost as much influence as exposure to shared opinions from multiple people. This finding shows that hearing an opinion multiple times increases the recipient's sense of familiarity and in some cases gives a listener a false sense that an opinion is more widespread then it actually is.
I'm sure a lot of people will be pointing to this regarding modern media, but this has firm roots in religion too, now you see why I worry about the zealots not letting their kids interact with people who have other opinions.