It's not a scam. When they make it blatantly obvious they're a Ponzi and people still feed them money, that's not a scam. People throwing money into 99% of these sites know exactly what they're doing and the risks they're taking as a result. If I tell you to give me $5 and there's a 99% chance I won't return it, and then I don't give it back, does that make me a scammer? Of course not. Why? Because you already knew the outcome. The same deal with Ponzis around here. I've yet to find ONE that wasn't blatantly obvious, therefore those that are stupid enough to send them money are not being scammed, they're just throwing away money.
If you told me to give you $5 and that there is a 99 % you will not return it then it isn't fraud because you've been upfront about the risk and I know what to expect. And I suppose a ponzi scheme that explains exactly how it works and the risks associated with it could be seen more as gambling and may be defensible.
However, the majority of ponzi schemes are not forthright with the fact that "investors" are being paid by later victims. They aren't forthright with the fact that it is impossible for the scheme to pay out forever. Instead, they market themselves as safe investments, often claiming there is a real business behind the scheme.
Now perhaps you and even the majority of the Bitcoin community are aware of this type of scam, but that doesn't lessen the attempted deception and make it any less of a fraud. And the sustained popularity of these schemes implies that there must be many gullible people that are not aware of what they actually are.
People need to stop playing the victim card and stop being so damned greedy. This is ridiculous. "I gave my money to some Internet stranger that promised he'll turn me into a trillionaire in just one month and he didn't. SCAM! IT WASN'T MY FAULT, I THOUGHT I WAS ABOUT TO BE THE FIRST TRILLIONAIRE ON EARTH!" *Continues on to the next Ponzi and repeats the same process, yet again crying because they lost, and then repeats it again and again and again in perpetuity*
I think it's fair to place blame on both parties. Leaving your car unlocked in a bad part of town may be stupid, but that doesn't mean it's not a crime when it gets stolen. Analogously, it's irrational for these people to expect any other outcome from a ponzi scheme, but that doesn't mean they aren't victims of fraud.