You don't need to take away people's purchasing power to encourage them to invest. If an economy is growing, there will always be higher returns in investment than in holding cash. Monetary expansion encourages unsustainable consumption and debt accumulation. Why is this preferable to saving? When people save, they don't do it with the intention of one day dumping the money in a lake. They are still going to use the money, just on a longer time scale for a better-considered purpose.
I don't want to take away people's purchasing power now, I want to sap away their purchasing power over time. If I do that I encourage them to take their money and invest it into a factory producing widgets instead of squirreling it away into a bank. Inflating the value of money gives an unfair advantage to people who use their money to improve the world by producing things. Being in debt sounds like an OK trade to me so long as it's not pathological.
