Whenever I see people defend the 40-hour workweek, I think back to this quote by David Cain:

'But the 8-hour workday is too profitable for big business, not because of the amount of work people get done in eight hours (..) but because it makes for such a purchase-happy public. Keeping free time scarce means people pay a lot more for convenience, gratification, and any other relief they can buy. It keeps them watching television, and its commercials. It keeps them unambitious outside of work.'