Zero Dollar Minimum Wage

From The Wall Street Journal, Opinion, "Then There's the Real Minimum Wage: Zero: Small business owners don't plan all those hours for little pay. Sometimes it just works out that way." by John H Heyer:

Amid all the national discussion about raising the minimum wage, it's easy to forget that there are thousands, if not millions, of Americans who work for less than the minimum wage—some even for negative wages (imagine that). Principal among these less-than-the-minimum are self-employed workers, tradesmen and women and small business owners, especially those starting new businesses.***After covering overhead, including minimum wage for their employees, small business owners may end up losing money—i.e., making negative income. How much is that per hour?***The largest category of zero-salaried workers are the millions who volunteer their services and expertise for nonprofit organizations—churches, YMCAs, schools, hospitals, kids' sports leagues, recreation programs; the list is endless. So it's OK for them to work for $0 per hour, or for the minimum wage, but illegal for anything in between. Does that make sense? If they can agree to work for $0 per hour, why not for $1 or $5 or any other number agreed to? [Emphasis added.]