I think the reason why this set of people are still thinking this way is because they have not done their research about what Bitcoin is all about, they just believe since it is something we use money to invest in online, then is Ponzi scheme.
Anything you really don't know do research about it before giving your concussion so people won't see you as a fool or you won't end up losing a life time changing opportunity.
Mindset is everything, and if you don't crave knowledge, you will just be controlled by your mindset. The understanding that people have towards Bitcoin will determine their interest in it. Ignorance has been a serious problem for people criticizing what they do not know about, instead of doing some research to understand what Bitcoin is all about.
This ignorance about Bitcoin has made many people disinterested, and after a long time, when they finally understand what Bitcoin is, they regret their ignorance. Ignorance will always set one back; that is why it is important for people to have the zeal to seek knowledge. What you don't know will always have a different meaning to you, which can lead one to miss a very good opportunity.