There is one important sense in which such things are different from
"money", in that they cannot be created by fractional-reserve lending.
But even when one agrees on a commodity for exchange, the convenience
of abstracting it is so great that it can't be avoided.
In the neighborhood of my grandmother's farm in Alabama, the common
unit of exchange was the egg: people would mow a lawn or weed a garden
for a dozen, trade a dozen and a half for a bushel of tomatoes, etc.
Even there, it was common for folks to draw up IOUs in terms of eggs,
and never pay them off in actual eggs--just tear up mutual ones, or
trade them for something else. Yes, they did trade other people's
IOUs, and honor their own whoever presented them for collection. I
don't think it ever occurred to any of them that they could "loan"
eggs they didn't really have by giving IOUs, but it might have.
"Money" is nothing more than an agreement among individuals to abstract
some valuable for convenience of trade. Those who oppose the idea are
just being stubbornly anti-social.