That right there is really the heart of the problem.
A coach who is volunteering his time doesn't need to have parents complaining about his methods and decisions, and surely doesn't need a parent calling any of his decisions "stupid."
That's why I hate the whole idea of having parents involved in organized sports for their kids. No offense, but if I'm a coach of a Little League team, the last thing I need is some @sshole who sees me as a free after-school program for his kid telling me that I've made any "stupid" decisions on a baseball field.
Well the, happy coaching!