A little moderate deflation is not bad. There was continuous economic growth with deflation in the USA after the American Civil War for ~2 decades.
Macroeconomists really have no idea what they are doing - except, I believe them that a sudden drastic drop in the money supply is bad
This is why people think a little moderate inflation is good for an economy, and deflation is bad. A currency needs to be spent to be of use, but if it is going to always increase in value, the sensible thing to do is to spend something else and keep the increasing currency as a nest egg. Unless you can mandate everyone only transact in Bitcoin, people will tend to spend other things and hoard bitcoin if it keeps increasing in value.
[1] https://en.wikipedia.org/wiki/Gresham%27s_law