Barter is just a bit impractical. It takes a long time, and a wander round Tescos with two shopping trolleys (one for the stuff you're buying, one for the stuff you're selling) could take longer than the half hour most people allow. It also has slight problems of localisation- for example, US mid-west farmers might only have wheat to barter with each other, while London City office workers could only give each other promissory notes, which don't make good eating. On the other hand, we'd get back the fun of sailing 2000 miles in an open boat, fending off pirates with the spare hand.

But look at gold (and other money) in a slightly different way. There's no need for the value of money to even approach the value of goods in circulation, because it can be used many times over. For example, a car engine might weigh 150kg, but only contain 4kg of oil, because the oil gets circulated many times (my van is 1994, but the oil is a GENUINE 1996).

And if you think a copper-plated steel disc is worthless, what about your plastic card?