The guy on the corner selling counterfeit Gucci would certainly argue that there isn't.
Whether a venture is successful or not has no bearing on whether a venture is a scam. Scams can fail. Like Fyre Festival.
Cryptocurrencies, and the sub-scams that are derivative from them, are scams because from top to bottom they require dishonesty in their presentation. This starts with how crypto - regardless of "which one", is marketed. Crypto, prospective buyers are told, is a functional alternative to national cash-currencies. It's money that the government and corporate interests can't dip their fingers in, free from regulators limiting your profit potential, private and nearly anonymous. The distributed and decentralized nature of the blockchain makes it hacker-proof and robust against bad actors trying to steal money.
In truth, all of these are lies, either positively or by omission. It actually has no inherent value whatsoever; the value of a whatever-coin lies strictly in how much "real" money you can trade it for when the time comes to cash out, so it isn't actually a functional alternative to cash currency at all, it's just another security. Nothing is stopping corporate interests from buying crypto and even influencing its value just like any asset based on cash money (e.g., Elon Musk), and the unregulated nature of crypto only means that such actors can freely do things they would go to prison for the rest of their lives for if they were doing it to cash dollars directly. Even the myth that crypto is out of the taxman's reach is at best a wilfully-blind fantasy, since the taxman has no problem simply waiting until you cash out - which you have to do eventually, otherwise your "crypto wallet" is nothing but an idle-game. And as far as security - well, anyone who has your Etherium wallet address can drop anything they want into it, including an app that will clean you out completely if you so much as look at it to see what it is - and there's literally nothing you can do about it if it happens.
The suckers who believe the lies and buy in will find out about all the warts eventually of course; but they're pressured and/or shamed into ignoring them....because that's just "fud", and you don't want to spread fud, do you? That would be a loser mentality - lol, have fun staying poor!
But yes; I feel quite comfortable generalizing cryptocurrency as a scam because it unabashedly uses all the same structure, language, and marketing of a superjuice MLM, to include using shame and peer-pressure to suppress reasonable skepticism and criticism among members.
