Ponzi schemes promise high returns, The Steem blockchain does not promise anything, Ponzies require that you "invest". You are not required to invest in Steem to earn the currency. The Steem currency itself has value:
1-Three second confirmations of transactions (irreversible in about 40 seconds).
2-No transaction fees.
3-Built in escrow capabilities on the blockchain.
4-The blockchain can handle thousands or tens of thousands of transactions per second (if not more).

To solidify the value of the currency (and not depend on the speculative value of it) the community needs to start using it more and more as a payment method for goods an services. And also direct Fiat bridges need to be opened.