Either way, Ponzi schemes can be very profitable. I don't think there is anything unethical about gambling with a Ponzi scheme.
Do you find anything unethical about early adopters defending Ponzi scams so that more people buy in (so that they can get out before it disappears)?
Do you find anything unethical about running Ponzi schemes, and trying to get as many people to buy in before you skip town?
As long as people understand the risks, then no. There is nothing unethical about it. Just like there's nothing unethical about encouraging people to play slot machines.
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.
From what I've read, "investors" aren't being mislead about where their money is going. They simply aren't being told to a satisfactory degree. That may be splitting hairs, in your book, but this is a classic example of "buyer beware."
Obviously some people are pretty happy with the arrangement. Some aren't.
With all the information available here and elsewhere, I think you would be hard pressed to say anyone is being "scammed" when people are voluntarily handing over their money based on the info they receive. If this turns out to be a bust, the "investor" has absolutely nobody to blame but himself.