People tend to comment what they do not understand. A Ponzi scheme is illegal. Bitcoin has undergone regulations and is accepted by any structure. It is investment and people can earn money with it. With any kind of investments, you can lose your money. It does not mean that all investments are a Ponzi scheme. Moreover, as many have quoted, the blockchain technology has nothing to do with a ponzi scheme. It is very transparent and useful to the society. It is not only about money. It can be used for different social aspects.