I agree with flarays and coachtea that there are a lot of good and fair parent coaches out there, and that some non-parent coaches aren't very good, so it's critical that a parent does their homework re: coaches.
My DD recently completed her college career, and has been interested in coaching the game for several years. She was approached by a couple of organizations about head coaching, and was flattered by it. Please keep in mind that some organizations like to brag about the fact that they have ex-college players coaching. But similar to other college and professional sports even, just because you played a game at a high level doesn't automoatically make you a good coach. My DD realized that she still had a lot to learn about coaching, and has spent the past 3 summers and winters helping myself and the coach we are both assisting now, and admits she is learning so much more. I think some day in the not too far distant future she is going to be a heck of a coach, but she will have put in the time and effort to get there.
I personally think a non-parent is an "advantage", but that opinion is biased and you've got to do your homework.