Yeah, I publicly admit that people LOSE MONEY ON PONZI. They can also win.
This full disclosure makes ponzi NOT A SCAM.
If things were as easy as that, then why are numbers rackets illegal?
It inhibits the state's ability to collect their share. They rather see the poor spending money on booze and paying a sales tax than have them gamble it away. In addition, they want a monopoly on their "official" lotteries.
Anyways, in general, it's for the same reasons that harmless drugs and victimless crimes are made illegal.