This is all unsupported by any evidence. The "deflationary spiral" theory is as wrong as its sister, the "inflationary spiral".

Inflation benefits borrowers, hurts lenders. Deflation hurts borrowers, benefits lenders.

The sweet spot is 0.

The reason everybody believes that inflation is good for you is because of persistent government propaganda to sell that idea, because what inflation really is is a tax on your money. That's right, a tax.

Now, if you want to argue that the inflation tax is a reasonable way for the government to raise revenue, ok, but be realistic as to what it is. Inflation isn't good for you any more than taxing you is good for you.