Earlier quoted context omitted.
When you have a growing economy but a fixed money supply, money will appreciate. When this happens, people will prefer to keep money rather than spend it, and you get deflation-induced recessions/depressions. See the latter part of the 19th century in the US for repeated examples of this.
What's wrong with that though? So people will end up not spending money unless it's very valuable to their lives. So less money gets spent on Angry Birds, iPad Minis, and games. Makes entrepreneurs have to up their game if they want people to spend money on them.
People on the bottom rung end up spending all of their money, and will find it even harder to ever dig their way out. The top 1%, who cannot spend money fast enough to exhaust it, will hold onto their money which will become exponentially more valuable over time.
Capital investment will plummet, because statistically, you're better off simply holding your money. It's like holding an index fund in the stock market (your money increases with value correlated to the market), except there is practically zero risk. Any investment you make by definition will perform on average no better than the economy as a whole; so why bother investing your money with risk, as opposed to holding onto your money with no risk? They both have the same expected value.