For people who are OK with keeping their money in banks but want to take it out as cash so they can spend it anonymously (as opposed to those who want cash beca

For people who are OK with keeping their money in banks but want to take it out as cash so they can spend it anonymously (as opposed to those who want cash because they don't want to have anything to do with the banking system at all) it is possible to design a system that retains the anonymity of cash but has the convenience of digital currency. And no, this does not require a blockchain. Long before Bitcoin, back in the days before cryptographic currency meant you were probably dealing with geeks bearing grifts, cryptography researchers developed digital cash systems. One I remember worked like this. Banks could issue digital dollars in multiple denominations. To spend a digital dollar D you would do a transformation on it to produced an altered digital dollar D' that you could give to someone. They could verify that D' came from a legitimate digital dollar, but got no information about which digital dollar it came from. When they deposit D' the bank could tell that it was generated from a digital dollar they issue and the denomination but they could not tell which digital dollar it came from. So even if the bank kept a record of every digital dollar you withdrew they could not figure out that D' came from one issue to you, let alone which particular one it was or when it was issues. If you tried to double spend by transforming D to produce D' and then did that again to produce D'' you would get two seemingly different altered digital dollars because the transformation includes a random factor. However if you spend both D' and D'' when they get deposited the bank is able to combine them to recover the original D and can look up who they issued it to and then you've got a lot explaining to do.