tl;dr: I don't want to work 16 hours a week and then sit on my hands for the other 30. I want to work 16 hours a week and devote the rest of my time doing things that enrich myself and my community in a tangible way.
I've worked for Google, Salesforce, and an early stage startup. In none of these companies did I feel like I was making a meaningful contribution to humanity. Either the product was of unclear societal value (Enterprise CRM), the work was so far removed from the value that the link to benefit was tenuous at best (second tier technical support for AdWords), or the ultimate results were no value generated (early stage startup where we scrapped everything after 20 months of development).
I've also taken gaps between jobs to focus on my own goals. In my free time I have volunteered with local food related organizations (serving meals in a soup kitchen, tending a community garden, etc), developed an iOS app used by 3,000+ artists, and bolstered my relationships with my wife and family. I've also taught myself several programming languages, enriched my world view through extensive travel and reading, and improved my personal well being through exercise.
In my opinion the contributions I've made through these "non-work" experiences and projects dwarf anything I've done working 50 hours/week for a salary.
It's possible that there's a job out there that would pay a decent salary and give me a similar sense of having made a contribution, but I haven't found it yet. I recently co-founded an ed-tech startup with this goal in mind, but time will tell if I'm able to move any needles.