>But of course they do, because if they didn't then they could just take the "free" money and still volunteer to do the useless work. Maybe some people like digging holes and filling them back in -- it's good exercise.

This is happening in practice. There are lots of popular jobs where people will put up with anything to get the job. Game developers routinely have "crunch time" but they don't quit as a result. Some even think it's a bonus because they get to spend more time at their dream job.