This is kind of like celebrities. Once they get famous, they feel like they need to tell the whole world what it should be doing. Most writers however aren't famous. And even if they were, having an agenda can get pretty old pretty fast.
Having said that, I've known authors argue both sides of this. I know some authors who simply want an adventure for the reader to lose themselves in. I've also known many authors who want their novel to bring a particular point to light.
The truth is, that whether you want to make a political, moral, or other type of point in your literature, the reader is often going to take something away with them. You may just be writing a techno-thriller, but you may get them thinking about the ethics of technology or you may have them walking away thinking that in the future, casual sex will be so socially acceptable, that everyone should engage in it. You may even get them thinking of something you never even mentioned, but that came about as a consequence of your novel. For example, they might turn into conspiracy theorists because your shadow organization seemed plausible to them.
The thing is, everything you write, will say something of what you believe. The question therefore is: Do you actively control and plan what that message will be, or do you just let the story happen?
I subscribe to the camp, that you must control the message. Primarily, I want to write a book that entertains. But I would consider myself a poor steward of your time, if I put little thought into what you took away with you. As I've said, you will almost always take something away with you.
When I begin a book, my thought process goes like this:
1. Cool idea.
2. How can I turn this into a story?
3. When the reader closes the book, am I comfortable with what they take away with them?
4. I sure hope I'm not the only one who likes this book.
As you can see, I'm not trying to pound a point into your head. Nobody likes a preachy author. I just want to be responsible with the most important thing you've given me. Your time.
Thank you for giving my books a chance. I hope you enjoy them, and that when you finish reading them, you can sit back and say, yes, that was a good book.