You ever been to one of those food plaza places where you have to top up a prepaid card in order to pay for the restaurants? Or bought chips at a casino? Or bought Chuckie Cheese tokens as a child to exchange back into "real" money when you're done playing? Stablecoins are like that for the DeFi world. Places like Gemini/Coinbase are the legal onramp. You exchange official money for crypto there, trade it for chuckie cheese tokens, move it out to some other "web 3.0" property operated from god-knows where, then do DeFi stuff there and when you're done you do the above in reverse.