Btc is NOT a ponzi scheme and anyone who calls it one either doesn't understand what a ponzi scheme actually is or doesn't understand btc - likely both.  Btc MIGHT be a pyramid scheme - that is at least worth discussing, but not ponzi.

Key differences - pyramid schemes CAN be legal (multi-level marketing etc) while ponzi is not
participants are aware of, or can be aware of the situation in a pyramid, in a ponzi there is deception over what is really happening

Anyone who calls btc a ponzi should really just be ignored as a fool.