Writing What You Disagree With

It is generally accepted that every character is an extension of its author. It sounds good, but I wonder how a person can create characters with very different personalities and beliefs.

From my own experience, I've found that I can write conflicting characters because I can take both sides of the argument. Sometimes, however, I come across an argument that I can only take one side of. What do you do when you can't take both sides of the argument? Does that mean that all of your characters agree on this one thing? That doesn't sound conducive to good writing.

The best answer I've found is to get out of your head. Instead of trying to win the argument, your characters have to have the argument. Even if you yourself think the argument itself is so stupid that it shouldn't even be made, other people disagree. If you want your characters to be realistic, they at least need to talk like real people do. They need to make the arguments that don't make sense and believe them. They need to say the things that sicken you and do it with conviction.

I think that this is how you truly make characters, to know them. While you can create a great deal by borrowing from your own thoughts and beliefs, your Dramatis Personae will only be so large and will eventually be stunted because of it.