Actually the early investors simply participated (unknowingly of course) in fraud. You can say "well we thought the deal was legitimate" but if it was a ponzi, then the statement "the early investors participated in fraud" is accurate.
Sorry for this example, but i don't know how to comment your post..
"...if that was a rape, then the statement "this lady participated in rape" is accurate."
The person who runs the ponzi is 100% culpable, no question. And yes, one of the hallmarks of a ponzi is to encourage investors to re-invest their "profits" in buying "more shares" or "hashing power" or whatnot. That keeps the initial investment in the ponzi system as opposed to leaking out.
Sorry if I was a bit unclear.
Maybe this example was not to good, because i was expecting that you gonna explain that.. But here was late and that was first what comes to my head ..
This is how work Ponzi in Bitcoin world. Trendon Shavers showed the way.