People seem to put forth the argument that "people will work more efficiently if they work less hours" to counter the argument "if less time is being worked, then less work is being done, then costs/prices go up". And, while it may be (and probably is) true that efficiency will go up, it's almost certainly true that overall work will go down (because efficiency will not go up enough to compensate for the loss of work time).

Now, the/your argument that the overall loss in work is worth it for the work/life balance benefit is one worth considering. It's just a different point from the one that that less work, overall, will be done, likely resulting in higher costs. I guess another way to look at it might be

- Am I willing to earn 10% less in exchange for working 20% less?

And, as a reverse example for the 6-day work week

- Am I willing to earn 10% more in exchange for working 20% more?

For me, at least, the answer is no to both, because I'm comfortable with my 5 day work week. For some people, the answer to one or the other of those is yes.