On working for free

Recently, this comment was left on my job posting for a book designer:

You know what they say, Mr. Berkun – you pay peanuts; you get monkeys. If you want someone to spend the time required to design a book and then not get paid with anything other that good wishes, you're on the wrong track. Would you do consulting for free if a company said they would give you freedom and publicity alone?

There is nothing disrespectful about asking people to work for free if you are doing something interesting. Here are my arguments:

There are kinds of compensation other than cash.  Sometimes those other rewards are harder to obtain than cash. If you were a guitarist and could play a gig with U2, without pay, would you do it? I'm sure you would. I'm not Bono in 100 different ways, but you get the point. If you think I'm a bozo, I wouldn't want you working for me simply because I'm paying the most.
Yes, I work for free when the rewards are worth it.  Most experts or famous people do. If ever you see some author/expert on a television show, I guarantee you, they are not being paid to be there. Why? The opportunities of that "work" have value above and beyond financial compensation. I do webcasts online, for free, quite often.
If I could work with someone I admired, on a fun and challenging project, I'd certainly consider doing it for free. Especially if the project was unlikely to reap financial rewards for anyone involved (such as, say, an experimental self published book).
Hell. This blog you are reading is "free". No one pays me to do this. So why bother? Because it has rewards I can't obtain any other way.  I'm a writer by trade, yet I've written 1000+ posts here. Arguably 70% or more of the words I will ever write I will not be paid for.
Specific to this designer role, I don't want to hire someone who is motivated for this project solely for financial reasons. I did mention I'd like to find a way to pay them, but can't promise.  Primarily I want to hire someone who a) digs my work and wants to collaborate, or b) who is motivated by the opportunity to design something amazing and recognizes the unique opportunity here – since in the publishing world, designers rarely get that kind of seniority on a book with an established author.

The zero-tolerance argument against working for "free" is a bad argument, as zero-tolerance arguments always are. It discounts non-financial compensation, puts no value on how interesting or exciting a project can be, and ignores the huge number of successful people in hundreds of fields who willingly choose to work on projects without pay.

So fine, you can call me a monkey. I like monkeys. But at least in this case I'm a monkey who is practicing what I'm preaching.