Imagine an empty room. A few people come in with money in their pockets and play a few rounds of a card game. When they leave, since nothing was in the room before and nothing is in there after, it's obvious the total sum of money couldn't change. Some got richer, some got poorer but the total is the same.
If they decided to exchange money for plastic chips to be used during their games and exchange it for money at the end, the same is still true.
However, if someone takes a cut every time chips are moved then that person is guaranteed to win and the players in total are guaranteed to lose. If you have a game where you know who is the winner and who are the loser without knowing anything about the game, I believe it's fair to call that a scam.
No, stocks are not like this because they produce dividends and gold is not like this either because there are consumers (jewelers, electronics industry) who buy gold add value to it and only sell the value added product. With a crypto"currency" none of this happens. You buy coins, sell the same and they just rot ("HODL" in modern parlance) meanwhile. And you lose money on every transaction. Sure, the price change might mean you leave with a monetary profit but it only means a greater fool is now sitting on a larger loss.
This is a very novel scam for many obvious reasons but that doesn't mean it's not a scam.