I was listening to a webinar a few weeks ago when they were discussing social change through our writing.
The first book that came to mind was The Chamber by John Grisham. I saw the movie before I read the book, but the one thing that stood out in my mind (in the book version) was that John Grisham didn't preach about capital punishment.
In fact, by the end of the novel, he set the moral implications of capital punishment on a silver platter, as if presenting both sides of the coin.
The novel gave us a choice. Both sides seemed plausible, no matter what side you stood on. He didn't preach one side over the other, even if he did hold a certain view. The reader just never saw that side of him.
I've read books where the authors preached their social views on issues to the absolute extreme. Whether I believed in the issue or found that side completely absurd, preaching has always grated me the wrong way. Even if I believed it.
If you have a story, tell it. If there are issues you want to address, do it through story. You may actually sway a reader to your side if you tell your story, through the actions of your characters, well enough. Take as an example: The Hunger Games. Suzanne Collins did a wonderful job of portraying the grim realities of a post-apocalyptic life and the greed of a totalitarian system. Not once did she preach that the big bad government was horrible and should be stopped. She told it through the story--and through the other two novels in the series.