Of course, even collateralized loans to buy real estate are not, despite what you said earlier, risk-free--see 2008 (and google the term "CDO", in case you've never heard of it) for a rather dramatic example of this.

More to the earlier point, though, this is really not how most lending works, so the idea that this somehow means that "absent central bankers, we'd all make 2% APY risk-free on bank deposits" is just silly. The global equity market is $50T, the global corporate bond market something like $100T. Total cash-equivalents (M2) in the US is $21T.

Even if "pledging shitcoins as collateral for speculating on coinbase" were zero-risk--which of course it isn't--the market for such loans is, unfortunately, too small for all of us to retire risk-free.