I've been reading Writing the Breakout Novel, by Donald Maass, and he says you need to ask yourself why you are writing this novel. If the answer is something like "for the money" -- not a personal, internal reason -- then you're writing for the wrong reason, and it won't be the best book you could write. It will lack something important -- conviction.
He also says you should write about what you believe in, what you care about. I think that's a good point. Your beliefs will come through no matter what, so why not encorporate something in from the beginning?
That said, I don't like to write "issue" novels. And I don't believe he's advocating that, either.
But I do like to include things I can really care about in my writing. And when I don't, there is a different, as Maass says.
Anyway, what I've read of this book so far is excellent. You should consider checking it out if you're a writer.
~Alice M. Roelke~