I don't think there are many places in tech where an employee can leave at 5 and expect to keep their job.

I politely disagree. If you think “hours spent at desk” correlates with performance, I don’t really know what to tell you.

I do work late, and over my career have absolutely pulled all nighters and weekends and been on the redeye, but that’s when I stretch or flex, and it’s simply not sustainable.

Of course there are. In my 20 years of experience I've never worked in a place which would expect people to work overtime. (this wasn't in my selection criteria BTW)

There absolutely are, but they aren't startups.

I've always been somewhat flexible, especially when traveling, but I've pretty much never worked super-long days as a routine.

You've been brainwashed.

Not true at all.

Ironically, it's only junior engineers that haven't learned how to say "no" that I've seen hold this opinion.

Most of people I know work 37 hour weeks and use sone kind of flex system where hours above 37 per week are saved and spent at later time. The only person keeping track of your time is yourself.

Isn't socialism great?

I don't work for free and neither should you.

As an entrepreneur, you can leave anytime you want, but of course, you can't leave the responsibility aside.

With an employer not offering remote, you can set your own rules around it. You can work from Bali, if you want and your customers are OK with it. But i agree , the small business route is certainly not for everyone.

Not to mention the existence of society literally depends on massive large coordinated efforts. It would be completely impractical to operate a society where everyone was an independent small business owner. Imagine trying to operate the global logistics system, or plan, build and operate off-shore oil wells. Being part of a team is a valid and honorable thing.