of course its not just for ponzi schemes. Other traditional financial crimes are possible and common , as well as financing of embargoed countries and criminal groups. So much possibility! Clearly a growth industry.
Put dollars into your mattress then. That's more secure. The value should be denominated in USD anyway, but in many cases isn't. Often the price is listed as BTC/USDT with USDT being yet another shady enterprise where part of the financial backing is from the value of BTC.
without the illegal use cases to pump up the value of the coin, you're basically converting your currency to digital IOUs that fluctuate in price and there's no reason for them to have any value at all. The thing that gives all of these coins values is speculation due to all the scams and illegal money moving.
one is a non expiring real world good with uses outside of speculation, and the other is a digital certificate of ownership of a number on a blockchain. If you truly cannot see the difference between the two, no one can help you.