Field studies have been conducted in several countries now, and the result is always the same - people will just flop about for a couple of months to recover from the burnout most people who have a job live with, and then they look for something to do. Some get a job with reduced hours, and some start doing charitable stuff like volunteering in soup kitchens and teaching others to do whatever their particular skill is. They socialize more, they are happier, and on average, people will work more, not less.
But the thing is, employers suddenly have to think about how to make their jobs appealing enough for someone to come and do them! It's hard to find someone to work for you for long hours under horrible conditions, if they can just choose not to; which shows you how voluntary our current system actually is.