You work for a large, for-profit company. You have some free time outside of the typical 9-5 M-F work week and you would like to spend some of it working. Great! You could:
* contribute to an an open source project or start your own
* start a side project/business
* volunteer somewhere
* take an online course
* exercise
* goof off
* do almost anything else
The effects of these on on society and yourself range from neutral at worst to helpful at best.
Instead, you choose to:
* contribute extra unpaid time to your employer
This may enrich your life, but it definitely enriches the shareholders of your company. It dials up the expectations of others who are in the same employment pool as you. It hurts future generations of workers by eroding the expectation of work-life balance that we are lucky enough to have achieved in our industry.
To me, it is pretty clear: if you put your extra time into for-profit work, you suck.