The fact is that everyone is entitled to their own opinion, that they call Bitcoin a ponzi scheme doesn't change any thing about the originality of Bitcoin. Such people have little knowledge about how the Blockchain technology works, they need to be enlightened
Of course until they fully understand about Bitcoin and its blockchain network people will call bitcoin a fraud or ponzi scheme and it is normal for them to say that but once they understand about the true nature and potential qualities about Bitcoin the view might change for better but for this ti happen it might take several years because still the amount of people who benefit from Bitcoin are much less considering the rest