This current frenzy only proves that a "deflationary spiral" cannot be permanent

Unless you believe there is such thing as a permanent asset bubble (there is not), you cannot believe in permanent deflationary spirals. A deflationary spiral is simply a bubble for money. People "hoard" securities during bubbles, and money is no different.

So unless you believe in bubbles that literally do not end, you reject the notion that central banking is required to expand the money supply to stop deflation.

And let's say this isn't a bubble at all (it may not be). That means mass adoption will occur and BTC takes a bite out of the fiat market share. so the speculation was rational and justified.

A currency with around 100% adoption rate cannot have this luxury; mass adoption has already reached its limit, and it can only be a bubble.