The point is that it's good for a company to be willing to discuss these things. If Signal had a culture where the principles and direction of the company are beyond discussion, that'd be a problem - both because it would make Signal a worse place to work, and because it would make compromising the spirit of the principles much easier.
It's probably helpful to look at a less emotionally charged principle like "customer focused". If your company enshrines "customer focus" as an inviolate principle, and nobody's comfortable discussing the value or meaning of "customer focus", you won't end up with a laser focus on the customer. You'll end up rudderless, because anyone skilled at office politics can justify whatever they want to do by declaring it customer focused.
It's probably helpful to look at a less emotionally charged principle like "customer focused". If your company enshrines "customer focus" as an inviolate principle, and nobody's comfortable discussing the value or meaning of "customer focus", you won't end up with a laser focus on the customer. You'll end up rudderless, because anyone skilled at office politics can justify whatever they want to do by declaring it customer focused.