You're right. There's no such thing as universal concerns or interests, or the general "human condition." Only an author of the same ethnic group, gender, race, religion, economic class, or handicap-status as the subject can write insightful fiction.
Oh my, you're so clever it seems you've missed the point entirely. It's okay for a given writer to write about any subject as long as he/she maintains integrity, even when writing fiction. Take a look at good fiction, Steinbeck for example, and you will find the authors are masterful at telling the story of their characters from a perceptive (outward) rather than from projection (inward) view. It's okay to describe a character of a different race or gender from a perceptive viewpoint when outside the group, but it's dishonest to write as though you're that race or gender and this is how I actually think. Can you discern the difference? Why do you suppose the author of the Potter books needs a male character as a vehicle to promote witchcraft?