You can only be sure that bitcoin is not ponzi, but not the entire cryptos. Even with that there are people and establishments that also use bitcoin for ponzi schemes. It all depends. People use concepts differently and I do not see why it is a problem if they do same with cryptos. If we must say what is right, no financial investments gives the type of profit cryptocurrency gives. It has made many millionaire and set more free financially but people have to be careful going into it. Invest wisely to avoid regrets.