That's the established theory. This theory is based on the assumption that only growth and a expanding economy are good. If you look at Japan, which is in economic contraction mode since years despite money flooding by its central bank, the life of the ordinary people has not become worse. You have to consider that especially people with low income, who have less options to get attractive returns on their capital, may actually see increases in their relative purchasing power.
What's more: It's highly unlikely that people stop spending entirely in a deflationary setting. They just buy less stuff they don't need and take less loans. In fact, that's a good thing - for people and the environment, because less resources are wasted for artificial growth.
ya.ya.yo!