These people are even dumber than I thought. If a country forgoes its currency, it lacks a serious tool to trade with. It’s why any nation wanting to be recognized as sovereign has a currency. In theory, like most Marxist philosophies end up being, you can have a cashless society, but value will still be attributed to various objects, and used for trade instead, which makes it act as a currency. Gold will likely be valuable in even a cashless society because of its many uses, and the fact that it doesn’t tarnish easily.
I hate 'money'. I hate the idea of a 'store of wealth' that's also the 'method of exchange' that's up to market forces. But it's reality, and there's no better system. Even with Star Trek replicators there'd have to be some way to distribute works of old art or something. You can't have more than 1 original Mona Lisa to give around.
You'd end up back to a form of barter, which sucks on those types of things. Marx himself thought automation was making human labor obsolete (we're hearing that now with AI too, it'll just be moved around and some will fall out).
AI/robots/space may reduce the need somewhat, but there will always been limits and a need of 'value' that won't be 'equal'. People aren't 'equal'.
This illusion of 'people are equal' when we know they obviously aren't, between and across individuals, races, and genders is a major problem holding humanity in a bad zone. The acceptance of the difference of abilities is a hard roadblock.
ETA and you gotta remember, fiat currency is no different really than crypto, which are a bunch of people salivating over a bunch of SHA-256 solution results off somewhere you can 'own'. It's all angels on a pin counting. For most people 'money' is just a number that shows up on a website that they can send like an email to another person that'll have that number. And people will kill and die for those numbers because everyone's a bunch of suckers.
And the most materialist of all aren't the capitalists (I know materialism in marxism sense means non-religion mostly, but also just flat out commodities. It's all the same to them), they are the socialists and communists which presume to replace economic power with political domination. At least with economic power there's some hint that there's value behind it.