If you were in my shoe, what would you've told a person that says bitcoin is a ponzi scheme created to scam people?
I would just tell them that Bitcoin is a crypto currency and nobody could guarantee that they would earn if they invest or buy it,
Just like holding other currency or trading forex it is the same in crypto but the only difference is Bitcoin is decentralized.
So if there would other person who would guarantee them a profit by investing there is a huge possibility that it is a scam.