You didn't understand my point. I am not talking about people's unlimited demands or their needs. I mean the utility of money over barter (i.e. not the utility of things that can be bought with money). With barter you don't have as many options as with money. What you have for exchange may quickly deteriorate, other people may not be interested in that, you can't postpone consumption, and so on...
In this way money is not an abstract imaginary concept in the sense it is meant in this topic
Ok, I guess you mean the utility of enable transaction. Money indeed brings much more convenience than barter, but I think that the utility of transaction itself does not have any value, since it is some kind of knowledge. When it is discovered, it become free for everyone to use, it can be duplicated endlessly, you just need to find enough people to agree on one or several transaction medium
If you are living in a total barter society, the invention of money will increase the commercial activities a lot, thus bring great value. But in today's society, when the technology is already available, more types of money will not create more value (That's definitely diminishing marginal utility). Fiat money has lost the ability to store value in a relatively long time, thus some other type of money like bitcoin might come to replace its place in this specific area. But overall there are only 2 utilities of money: Enable universal transaction and maintain purchasing power for a long time
So you are essentially saying that the transactional utility of money is nullified (its marginal part), that is, any greater amount of money doesn't add up to it. Okay, this doesn't look contradictory, but this in no case means that the concept of money is useless. It is like saying that the air we breathe is worthless since its marginal utility is zero...
Exactly, knowledge is of course useful, and those deep knowledge can still have value due to years of time needed to learn. But the knowledge of enable transaction using money is very simple, almost a known fact
We can also observe this on bitcoin: Bitcoin is an invention that enabled so many things that can not be done before, like anti-copy and electronically transfer ownership without third party, so it has certain great utilities. But the blockchain technology can be widely spread, thus all the alt-coin will be able to enable exactly the same things, and those alt-coins will worth a little, since their marginal utility over bitcoin is minimal
Similarly, since fiat money already exists, most of the people can do transactions with fiat money, bitcoin does not really provide extra benefit in enabling transactions domestically. But it enabled instant international transactions, and long term store of value due to expansionary monetary policy around the world, that is the area it is mostly demanded today