Again, it seems like the effect of hoarding your money is to make goods and services cheaper for everyone else (because there's now less money chasing the same goods). That seems like a benefit to society rather than a negative externality. And that's why it's rewarded with increased purchasing power in an economy that uses sound money.
They're just arguing the broken window fallacy in reverse. If you contribute to society but don't consume, you're somehow hurting everyone else by not doing your part. We all have to break windows, lest all the window factories go out of business.