I tried to explain that with a non-backed asset, that is a potential outcome that is unavoidable. If people decide collectively that your coin is worth shit, it will be worth shit. No matter what mechanism.
The USD and pretty much every fiat currency in the world is non backed. They operate perfectly well. The point is, there are degrees of valuation; it is not as binary as your quote suggests it would be.
For example, you could imagine a BTC side-chain, which was a CFD market for BTC/USD. Shorts of BTC in this market could be issued as stable coin tokens, valued $1. As long as there existed sufficient liquidity this would be a tenable stable coin implementation which would indeed cope with a devalued BTC price.
By contrast, your proposition does nothing at all with devaluation, such that a value of $0.3 could exist forever (when it was supposed to be $1), making the idea of it being stable laughable.