It’s not “idle” if it’s being invested, either directly or indirectly. Even if it’s kept in a savings account, the bank gets to loan out multiples of this money.

Nothing wrong with “idleness.” Water before a hydroelectric dam is also idle. Theoretically, you don’t need such a big lake, so long as the height of the water column is tall enough. But it comes in really handy when there’s a drought.

Same with money. If people hold it, they can get through a recession (or voluntary period without work) much better. The notion that everyone should be working 50 weeks a year from age 21 to 67 is idiotic.