Late to the party, but we’re on an area I teach, so I thought I’d chime in:
Remember what investing means in this context. For the ABCT, we have something called the market of loanable funds, which means all the money available for business to borrow, regardless of how the businessman acquires the money. So, investment doesn’t just mean buying stocks, it also can mean buying a CD, or just putting money in a savings account, so that the bank has the money to loan out to business. Ultimately, it just means that the businessman can get money at a lower interest rate. The only way to consume less and not do this is to stick money under your mattress. And what happens if you stick money under your mattress? Your drop in consumption puts downward pressure on interest rates, and in the future you’ll have more to spend than you otherwise would have - so even this behaves just like investment.
Why do you save money? Spending money now means that you will have more money to spend in the future. Future spending vs. present spending changes not just the when, but the how of your spending. You put off current consumption for greater consumption in the future. So, instead of buying ice now, you’ll buy a refrigerator later - that is, a more expensive, more capital-intensive good. So when savings are up and consumption is down, businessmen had better be shifting resources to more round-about methods of production, which requires shifting labor to earlier stages and buying capital goods.
You later clarified this question to the Bryan Caplan problem with the ABCT - namely, if the Austrians get it, why don’t businessmen, when they have so much more on the line? A simplistic, although not entirely false, answer would be “they went to business school and had common sense driven out of them.” And, in fact, there are some entrepreneurs who see more clearly what is happening and tend to do better. On the other hand, just because the boom is artificial doesn’t mean you can’t make money off of it - or be left behind if you don’t. Were businessmen wrong to devote resources to building houses when interest rates were low (originally)? Clearly not. Another point is that the idea of “interest rate signalling” is Hayekian baggage which a Misesian wouldn’t really want. More than a signal, the low interest rate just is an opportunity to borrow more money at low rates. Also, just because the government is screwing with the money supply doesn’t mean that there isn’t real savings.
Careful there. It’s true that the monetary value of goods falls during deflation - but does that mean that the value of the good drops? The monetary price establishes a ratio - say a car is $1000, and a pizza is $10 - the important fact is the 100/1 car/pizza ratio. So there’s a period of deflation and the prices are $100 and $1 - but the value of the car has not dropped, since the ratio is the same.
So, I loan you $1000, and lean your car as collateral. You fail to pay, and now I take the car which is worth only $100. However, if I had taken the car initially, I could have traded it for 100 pizzas - and I still can. So what have I lost? Now, this is different from inflation, which doesn’t happen equally across the economy, because natural deflation - that is, when no one screws with the money supply - does happen evenly across all goods.
Besides, assume it did make it harder to give loans. Then interest rates would go up - and? As long as no one is screwing with the market, there’s no reason to favor one interest rate over another, and there’s no a priori correct allocation of goods and money.