A lot id said about "messages" and stories. Some writers believe stories should have a specific message; others don't. Whatever you might think, I don't think any writer can deny stories have power. They can reflect the world we live in; they can confirm our beliefs; they can challenge them; they can even change them altogether.
Personally, I think a story has a message whether the writer believes it has one or not, because of re/presentation. To me, a story is not *just* a story - even the choice of what you want to write about reflects who you are, even on a deep subconscious level. As far as I'm concerned, a story is not just a story, but a deep communication - whether a writer understands what that communication is or not.
As I look at the body of my speculative work, growing over the years in number, certain themes have become apparent. Whether these themes are entirely "accurate" depends on one's definition: someone who has read a lot of my work might make the assumption from certain characters I have written I am deeply suspicious of others' motives, even cynical. Yet other factors must also come into play - story choices like what is the most dramatic thing one can write, what "ups the ante" and so on. So whilst I am not naive, nor prone to rush into relationships with an open heart leaving myself vulnerable, I would say I am not cynical either. But then I would, wouldn't I? We all view ourselves differently to how others perceive us. According to certain people, I am difficult; to others I am easy-going. It's the same with all of us. As annoying as it is to sit on the fence, it simply just depends: it isn't an exact science.
However sometimes a writer will believe something SO MUCH they write it into their script with the intention of disseminating this belief to all who will read it, perhaps watch it. I've read scripts in which messages over homosexuality, racism, sexism, compromise, religion and more have hammered home with as much subtlety as a sledgehammer.
It doesn't work.
When characters have strong beliefs in your script and shout them from the rooftops at every opportunity, it invariably means one thing: they have become mouthpieces for the writer's own personal beliefs. As a result, it's hard to believe in that character - they seem more two dimensional, they're harder to relate to.
You have a good friend. You know him/her really well, perhaps you grew up with him/her or you went to school or university together (or both). Maybe you know their spouse, their kids, their extended family. Perhaps there have been moments in which you have had to "step in" and help them or they you - with money, relationships, other problems. You and s/he have known each other through the best of times... And through the worst of times.
Now, the alternative: a man or woman who stands in a central area of your town and preaches. It doesn't have to be religion; it could be against religion; against sexism; against racism, whatever: there's a chap in Bournemouth for example who stands in the square and shouts about the lack of family values in the world. Perhaps they give out leaflets, stickers or badges - perhaps they have music; perhaps they have a big sandwich board they wear or a big display they use to attract people's attention. And they do attract attention. All of us have seen these people.
Now, if both of these people ask you to re-evaluate your opinion on *something*, which one would you do it for?
I'm not saying street preaching NEVER works, for some people they can prove a revelation. I am willing to bet however for most people it doesn't work - even if they happen to agree with what the street preacher is saying. I happen to think the Bournemouth Guy has a point; it doesn't mean I've ever taken one of his leaflets though.
I do believe however "script preaching" never works. If you want to send out a message via your script, simply having a character recycle your own thoughts is not the way to go - you need to develop the character first, make us believe in THEM before we believe in what they say. It's also important to remember that if your character has a belief, you also need to give them ACTIONS to back this up - if they're just talking about what they believe, that's not dramatic. Instead, these characters will seem like they're ranting. Of course, every now and again a rant can be fun - if it fits the story and/or reveals character, like Donnie Darko's amusing monologue about Smurfs, or Miles' thoughts on Pinot in Sideways.
But not all the time.
Give us a 3D character and we may believe what you believe.