A no-cash system, beside all the other downsides, reduces and sometimes outright removes the ability for humans to alter and/or workaround the system when systematic failure modes are discovered. And that's just unintended consequences, forget about perverse incentives.

This is the same reason I think augments that posit privacy is unnecessary because enough downstream controls will somehow account for all "bad" things that could happen. It's a scam, pushed by unscrupulous hucksters for their advantage at the cost of everyone else.