Cheap hypersonics don't threaten global stability, they threaten global hegemony. Which is really what I suspect irks most people afraid of them.

We've seen a shift towards cheap offensive capacity that gives middle powers or even smaller actors the capacity to hit hegemons where it hurts, very visible in Ukraine and the Middle East now. This leads to instability only temporarily until you end up in a new equilibrium where smaller players will have significantly more say and capacity to retaliate, effectively a MAD strategy on a budget for everyone.

GP's point was broader than that, it was about technological progress and the possibility of terrorist groups or mentally ill individuals getting their hands on weapons that can easily kill millions of people. That's also what the paper I linked is about.

Consider a future where individuals can relatively easily engineer a pathogen or manufacture a nuclear weapon. It's not hard to imagine how that would threaten global stability.

History would seem to show that hegemony is stability? Pax Romana etc