Before I knew I was a writer, I had a conversation with a guy that went something like this:
Writer: How would a guy say that he doesn't like pizza?
NonWriter: Um, like that.
Writer: No, I mean HOW would he say it? Because, you know, boys talk different than girls.
Writer: Never mind.
NonWriter walks away shaking his head, probably thinking Writer is just weird.
A quick note about my bad high school grammar. Well, I was in high school and didn't know better. OK, proceed...
How NonWriters Can't Help Writers
Even though I didn't know I was a writer yet, I instinctively could hear that boys tend to have a different way of talking from girls. Using my pizza example, a girl might say, "Eww, how can you eat that? This pizza's disgusting!" but a boy would be more likely to say, "This pizza sucks! I'm never eating here again."
But nonwriters don't get the difference. So asking them is useless.
NonWriters Don't Get Voice
It's true that everyone has a unique voice, cultivated by years of culture, personality, and circumstance. Good writers train their ears to hear how each voice is different, and sometimes even guess why. Nonwriters don't really think about why they talk the way they do. So they won't be much help at the development stage of writing. You're better off asking another writer.
How NonWriters can help Writing
Once you have a completed story, and have asked all your writer friends to help, it's time to hand it to a nonwriter. Ask them to tell you what they liked and what they didn't like. This will point out problems that your writer friends miss. Because writers are great at helping you develop the characters, but nonwriters are great at taking each character at face value. Which is valuable, too. After all, ultimately your readers are not writers. (Well, not all of them anyway.)
That's my opinion. Let me know yours in the comments!
I write about, with, for, and around kids all day. (Well, maybe I do the dishes too. Sometimes.)