Ponzi schemes. Just like a HYIP site only those who are first will be paid and sadly those who joined late got scammed. Many sites does that, that's why we have trust issues on a site, we need assurance that they will last long. But nothing last forever aight? so that's why we need to be wiser than anyone. When you join a HYIP site just predict when will they run. And withdraw all your balance before they run.
They are here because they know nothing can happen to them. Bitcoin doesn't appear in the laws or Constitution, so we can do anything we want. There were many cases in which the FBI or so didn't know how to find them, so the chances of finding that guy is close to 0. I'm always skeptical when it comes to these kinds of websites. Always read reviews.
This is a free world, everyone uses his own "free will" to make choices and have consequences. I think this way is the most correct to live. Every choice has a consequence and we can learn from our mistakes. That is what happen when you invest in HYIP and Ponzi schemes. Sooner or later everyone learns that it's impossible to make profit with this kind of deal. You can have luck and make profit with one HYIP, but on long term it won't work.
So if it is a free choice of everyone and their responsibility to face the consequences as you say. But it also means that everyone is basically free to scam on their neighbor, and they shouldn't face any legal consequences for doing so. I'm more than sure that these scams and HYIPs include a point in their terms that they don't give any guarantees "explicit or implicit" as well as decline any responsibility for the possible loss of money.