Perhaps those who do not understand bitcoin think it's a ponzi scheme because they see promises of big growth, great rewards for early adopters, and because ponzi scheme is something they have heard of. He is right that early adopters stand to gain more, but then that's business.
The best counter argument is just to point out that the bitcoin economy is growing and diversifying. It's strengths are ease of use, price, privacy, and decentralization. Those are features that appeal to a global market and are in demand right now. Imagine what an entrepreneur in a poor country could do with a bitcoin phone app and a product to ship.
For those in the richer world, your paper money is going the way of the dinosaur. It's digital replacement will likely be much more expensive. For example; A dollar bill can be stuffed into a mattress, but a digital credit representing that wealth needs to be maintained. There is a cost plus profit associated with storing that credit and facilitating transactions. Consider how much it costs you to store and spend using your credit card vs cash. That is the digital future of your money.
The good news is Bitcoin!
