“I would rather try to persuade a man to go along, because once I have persuaded him, he will stick. If I scare him, he will stay just as long as he is scared, and then he is gone.” - Dwight Eisenhower
Just about any writer is trying to send messages, or convey ideas and/or concepts, in their stories. The worst possible way to do this is to say it outright. The most effective way to do this is to subtly convey it. A common paraphrasing of Ike's quote above is “The art of leadership is persuasion, not hitting the other guy over the head with a hammer”, and this really says it better than anything else.
If you are preaching too the audience then you are defeating your own goal. They don't want to be hit over the head with a hammer, and they will resist being hit over the head with a hammer. They will begin actively thinking of reasons why you are wrong, and an idiot. If, on the other hand, you subtly convey an intriguing thought or concept... you may actually succeed in your goal of the audience actually accepting your message as a part of their own way of thinking.
If you intrigue them and start a thought process by which they arrived at the conclusion you were wanting them too, they will accept it into their own way of thinking. If you try to preach too them and hit them over the head with a hammer, they will find excuses why you are wrong. So you are only doing yourself a disservice when you preach to the audience about what you want them to believe... that's the one thing they aren't going to believe when they are finished with your story.
"Leadership is the art of getting someone else to do something you want done because he wants to do it." - "Ike" again...