BTC is not a ponzi scheme neither is it a fraud, though people tend to use it to carryout fraudulent activities but it is far from being a ponzi scheme. If it was a ponzi scheme then it would have crashed a long time a ago since most ponzi scheme are being controlled by some group of persons, but btc is decentralized there  by allowing every individuals to take responsibility for all their transactions. Now that to me is what makes btc outstanding.