No, it certainly isn't fair to call it a scam. Cryptocurrencies and blockchain technologies in general are still in their infancy and as such today's cryptocurrencies are still highly speculative and potentially super volatile but there is certainly a huge future ahead for them. "Unlimited potential" is not too strong of a term. I don't really trust any of today's cryptocurrencies enough to seriously invest but I certainly think it is worthwhile to mine Gridcoin as I already use BOINC and to participate in the steem economy here. I like cryptocurrencies that serve a particular purpose beyond just being a currency. Steem may or may not survive in the long run but I don't think anyone is being misled about anything.