The crux of a Ponzi scheme, what makes it a Ponzi scheme, is that investors are intentionally mislead about where their money is going. They are told that it is being invested when in fact it is being used to enrich the scammer and to pay off earlier investors. They are told the fund is increasing in net worth when in fact it is getting more and more in the red. They are nothing like slot machines or investment risk. They are pure scams.

When you lie to someone to get their money, it doesn't matter whether they "understand the risks" or not. I understand the risk that I might get hit by a car when I cross the street, that doesn't justify someone intentionally running me over.