It's a great attitude to have, but it doesn't reflect my reality (maybe I should work on this). There are a lot of non-work, but not so fun things that I need to do--commute, cook meals and clean, exercise, home maintenance, errands, etc. I feel like my true free time is roughly 8:30-10:30pm on weekdays, one full weekend day, and two weekend nights. And I don't even have kids. Plus, I'm normally pretty beat by 9pm after work, so I'm more likely to veg out than work on some fun project.
To me, a 40 hour/week job just doesn't leave enough time and energy to devote to hobbies/interests/socializing. It's not that it's taking up 40 of your 112 waking hours (65% FIRED). It's that it crowds out the great majority of otherwise free time.