People who are convinced that coke is better and pepsi makes them puke are tools. Rather than thinking about it rationally, they take popular opinion and personal dogma and trick themselves into thinking that two things that are pretty much exactly the same (at least not different enough that one causes gastric upheaval) are significantly different (good for coca-cola by the way, economically speaking, its absolutely brilliant).
People who believe that the earth is flat are tools. Rather than thinking about it rationally, they take popular opinion and personal dogma and trick themselves into thinking that if you try to swim from New York to Paris, you'll fall off the face of the planet. I'm not going to bother holding your hand through the argument that preferences are opinions. Any graduate from Harvard law should know that everything is an opinion.
What links both of them is that they both have an opinion that is defended only by the fact that they are free to have an opinion. There's nothing wrong with groundless opinions, but in general, its unscientific to have them, which was why I was pointing out a very obvious example of stupid groundless opinions.
Btw, analogies usually compare two different things...the point of them is to illustrate specific relationships or similarities that is more easily understood in one than the other.