However.
This does not mean that all deflationary currencies are bad.
For example: It is entirely plausible that a currency which is almost 100% predictably deflationary would be preferable to our current currencies, the values of which vary depending upon many factors (central banking strategies, economic outlook, etc).
Whilst inflation may help spur consumer spending, and almost certainly does help the economy by permitting 'invisible' wage cuts to poorly performing workers/sectors (perhaps the biggest advantage of inflationary currencies, not even mentioned in the article), the upside of a nearly 100% predictable currency may be even greater.
Of course, it is also possible (likely, even) that our current central bank managed system is superior: The downside of unpredictability may be (likely is, in my opinion) outweighed by the flexibility granted to central banks.
But we'll never know unless we run the experiment.