Those people who keep saying that cryptocurrencies are big ponzi scheme are the people who doesn't have information about what it is. They are victims of misunderstanding and fake news. They will regret what they say if they fully understand what it is and its function.
We cannot avoid that there are people spreading negative news about Bitcoin,maybe those people have negative experience in Cryptocurrency or they don't have enough knowledge about it that's why they want to make Bitcoin become worst by spreading fake information.