I completely agree with this. For years, I was a crypto-currency advocate, telling any and all that it's better than their credit and debit cards. When I took a look at why, though, I realized that tool (in physical form) already exists: cash. As long as you trade a few with a few friends, or buy something from a Mom & Pop, no one can really know what bills you have, and there's no record, ever.

Every bill has a serial number. Social graph exploration of paper currency is possible with bill readers at only a few points in the bill life cycle.

If the same nodes repeatedly 'touch' the same serial numbers you can infer a relation.

You make it sound easier and more powerful than it really is though. For all intents and purposes, cash is mostly anonymous. Bitcoin, on the other hand, is traceable if you can map accounts to real people.

> no one can really know what bills you have, and there's no record, ever.

The only downside to cash is a central authority controls it and can devalue if they so choose. Other than that, I agree, cash is great.