The argument was that people wouldn't be consuming if their wealth keeps growing and everything gets cheaper all the time, and the economy would grind to a halt

The argument was that people wouldn't be consuming if their wealth keeps growing and everything gets cheaper all the time, and the economy would grind to a halt. It's the same thing with investments, and it isn't true. People can buy gold right now and sit on it until they die (in a few days), but they don't. People spend whenever they need or want something, which is the fundamental force that keeps the economy running, regardless of what type of money or wealth they possess.