Actually, in the early days of bitcoin, most of its critics called it a Ponzi scheme but i wonder how a coin that takes a long period of time for it to be profitable, will be tagged as a Ponzi scheme. Are ponzi schemes not platforms that promises quick and fast profits within a short period of time? Those critics were really dumb to think bitcoin was a Ponzi scheme. Though i don't blame them much because since bitcoin was born out of anonymity, they probably thought that it was a kind of scam project hence the reason why its creator was not known but however, thanks to the progress and growth of bitcoin over the years as it is now clear that it was never a scam project from the onset and it will continue to prove its critics wrong.