basic story is: I have crypto asset worth X. I go to stable coin issuer. borrow X in stable coin. they have matching X assets and liabilities. I cash out to tune of X. I now have X dollars. Yeah?
I don't think MakerDAO gives 100% loan to value, so if your collateral is worth X, you'd get N% of X in stablecoins, which you could go exchange for dollars, but you'd only be able to get your collateral back, i.e. your full funds, by returning N% of X in stablecoins.
I could be wrong, as again I've never interacted with MakerDAO directly, but I assume their LTV isn't 100%. There may also be other stablecoin issuance protocols that do things differently.