Well, in real-life, some people actually have NEGATIVE net worth, due to loan, debts, credit cards, etc.
One thing that's a wee bit like this HBD is some years ago, when Chris Baldwin was doing the web comic Bruno. He needed to borrow money to print some books (this was before Kickstarter; back in the 1/0 days, I believe.) He asked his readers if they would loan each loan him $100.00, and after one year, he would repay us $110.00 (interest rates were generally higher back then, too.) I was one of the supporters who loaned him $100.00. In return, I got a nice little hand printed card (still have it somewhere) that stated I had loaned him $100, and he would repay me $110 on (whatever the date was. This WAS years ago.)
Well, It all worked out for everyone. Chris raised enough to get his books printed; sold them all; made a profit, and paid back all his creditors--I assume. I know for a fact I got repaid the promised amount.
Yes, it was a gamble. What if the books didn't sell? What if something happened to Chris, like being hit by a truck? That actually does happen to some people...I happen to be one of them.
Essentially, all money IS a Human-backed derivative, if you think about it. It just spreads the risk over millions of people, instead of only one being.
Oh, and I don't know if any one's brought it up or not, but I'll mention it because it can be quite a thing to some folks. A very good reason for not having our currency completely backed by gold, is because there simply is not enough gold in the world (accessible) to sit in vaults and back the value of all the goods and services produced. And why should there be? Food has a value. Preparing food well has a value. Serving well-prepared food in a nice environment has a value. As long as everyone involved agrees (or mostly agrees) on the value of the little pieces of paper exchanged to acquire things of value, everything will work out. The only time you run into trouble is when something goes fundamentally wrong with the economy. For example, runaway inflation = awful situations like pre-WWII Germany, where the economy is essentially destroyed, and people are reduced to wheelbarrows full of (almost worthless) marks for a loaf of bread, or straight-up barter, which is really a big pain in whatever part of the anatomy you least prefer.
The U.S. economy isn't doing as well as it has in many past years, but it's not that hard to understand why. The deficit has grown enormously (mostly because we had a long, expensive, pointless war that turned previous years' surplus into enormous deficits.) A large deficit makes many people nervous, so they buy gold or other "hard" valuables instead of investing in the stock market (companies that make things.) Stock market slumps cause their own chain reactions. Essentially, if you think of the U.S. as a family that's a bit too close to maxing out its credit cards, doesn't have much in the way of savings, but is still making juuuust enough to pay the bills (at the moment anyway) that goes a long ways towards explaining stagflation and all that. Plus, the U.S. Federal Income Tax system has gone beyond ridiculous to Kafkaesque. (Economics really isn't all that hard. Try thinking of a country's situation as like a family's. It makes it easier to wrap your head around the fundamental things. Essentially, if a family's debt burden is too high compared to its income, things go right to hell. Same goes for a country.)
Anyway, the main reason a single Human-backed derivative is a bad idea is that it is relatively high risk. For both the human doing the backing, and the investors. If you really need me to explain further WHY it is so high-risk (sigh) I will, but please try to think it through first.
Or perhaps you like high-risk. Most humans are fundamentally risk-averse, but there are always exceptions.