You should save this comment somewhere and get back to it in ~10 years if you happen to be married and have a kid :) I'm not being snarky or anything, I used to think the same.
You'll soon realize that side projects, friends and hobbies are nothing to be compared with having a spouse, responsibilities and taking care of a young child or an elderly.
The grandparent post, when young and single, did not seem to have anything else to do than work. I am well aware that people with kids are busier than me. My point was that being young and single does not make it fair to your employer or anyone to expect ridiculous hours. I was just surprised that someone would willingly do it and have little else going on in their lives.
You'll soon realize that side projects, friends and hobbies are nothing to be compared with having a spouse, responsibilities and taking care of a young child or an elderly.